API

This part of the documentation covers all the interfaces of Flask. For parts where Flask depends on external libraries, we document the most important right here and provide links to the canonical documentation.

Application Object

class flask.Flask(import_name, static_url_path=None, static_folder=’static’, static_host=None, host_matching=False, subdomain_matching=False, template_folder=’templates’, instance_path=None, instance_relative_config=False, root_path=None)

The flask object implements a WSGI application and acts as the central object. It is passed the name of the module or package of the application. Once it is created it will act as a central registry for the view functions, the URL rules, template configuration and much more.

The name of the package is used to resolve resources from inside the package or the folder the module is contained in depending on if the package parameter resolves to an actual python package (a folder with an __init__.py file inside) or a standard module (just a .py file).

For more information about resource loading, see open_resource().

Usually you create a Flask instance in your main module or in the __init__.py file of your package like this:

from flask import Flask
app = Flask(__name__)

About the First Parameter

The idea of the first parameter is to give Flask an idea of what belongs to your application. This name is used to find resources on the filesystem, can be used by extensions to improve debugging information and a lot more.

So it’s important what you provide there. If you are using a single module, __name__ is always the correct value. If you however are using a package, it’s usually recommended to hardcode the name of your package there.

For example if your application is defined in yourapplication/app.py you should create it with one of the two versions below:

app = Flask('yourapplication')
app = Flask(__name__.split('.')[0])

Why is that? The application will work even with __name__, thanks to how resources are looked up. However it will make debugging more painful. Certain extensions can make assumptions based on the import name of your application. For example the Flask-SQLAlchemy extension will look for the code in your application that triggered an SQL query in debug mode. If the import name is not properly set up, that debugging information is lost. (For example it would only pick up SQL queries in yourapplication.app and not yourapplication.views.frontend)

Changelog

New in version 1.0: The host_matching and static_host parameters were added.

New in version 1.0: The subdomain_matching parameter was added. Subdomain matching needs to be enabled manually now. Setting SERVER_NAME does not implicitly enable it.

New in version 0.11: The root_path parameter was added.

New in version 0.8: The instance_path and instance_relative_config parameters were added.

New in version 0.7: The static_url_path, static_folder, and template_folder parameters were added.

• Parameters:

  • import_name (str) – the name of the application package

  • static_url_path (str | None) – can be used to specify a different path for the static files on the web. Defaults to the name of the static_folder folder.

  • static_folder (str | os.PathLike[str] | None) – The folder with static files that is served at static_url_path. Relative to the application root_path or an absolute path. Defaults to 'static'.

  • static_host (str | None) – the host to use when adding the static route. Defaults to None. Required when using host_matching=True with a static_folder configured.

  • host_matching (bool) – set url_map.host_matching attribute. Defaults to False.

  • subdomain_matching (bool) – consider the subdomain relative to SERVER_NAME when matching routes. Defaults to False.

  • template_folder (str | os.PathLike[str] | None) – the folder that contains the templates that should be used by the application. Defaults to 'templates' folder in the root path of the application.

  • instance_path (str | None) – An alternative instance path for the application. By default the folder 'instance' next to the package or module is assumed to be the instance path.

  • instance_relative_config (bool) – if set to True relative filenames for loading the config are assumed to be relative to the instance path instead of the application root.

  • root_path (str | None) – The path to the root of the application files. This should only be set manually when it can’t be detected automatically, such as for namespace packages.

• aborter

  An instance of aborter_class created by make_aborter(). This is called by flask.abort() to raise HTTP errors, and can be called directly as well.

  Changelog

  New in version 2.2: Moved from flask.abort, which calls this object.

• aborter_class

  alias of Aborter

• add_template_filter(f, name=None)

  Register a custom template filter. Works exactly like the template_filter() decorator.

  • Parameters:

    • name (str | None) – the optional name of the filter, otherwise the function name will be used.

    • f (Callable[[…], Any]) –

    Return type:

    None

• add_template_global(f, name=None)

  Register a custom template global function. Works exactly like the template_global() decorator.

  Changelog

  New in version 0.10.

  • Parameters:

    • name (str | None) – the optional name of the global function, otherwise the function name will be used.

    • f (Callable[[…], Any]) –

    Return type:

    None

• add_template_test(f, name=None)

  Register a custom template test. Works exactly like the template_test() decorator.

  Changelog

  New in version 0.10.

  • Parameters:

    • name (str | None) – the optional name of the test, otherwise the function name will be used.

    • f (Callable[[…], bool]) –

    Return type:

    None

• add_url_rule(rule, endpoint=None, view_func=None, provide_automatic_options=None, **options)

  Register a rule for routing incoming requests and building URLs. The route() decorator is a shortcut to call this with the view_func argument. These are equivalent:

  @app.route("/")
  def index():
      ...

  def index():
      ...
  app.add_url_rule("/", view_func=index)

  See URL Route Registrations.

  The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed. An error will be raised if a function has already been registered for the endpoint.

  The methods parameter defaults to ["GET"]. HEAD is always added automatically, and OPTIONS is added automatically by default.

  view_func does not necessarily need to be passed, but if the rule should participate in routing an endpoint name must be associated with a view function at some point with the endpoint() decorator.

  app.add_url_rule("/", endpoint="index")
  @app.endpoint("index")
  def index():
      ...

  If view_func has a required_methods attribute, those methods are added to the passed and automatic methods. If it has a provide_automatic_methods attribute, it is used as the default if the parameter is not passed.

  • Parameters:

    • rule (str) – The URL rule string.

    • endpoint (str | None) – The endpoint name to associate with the rule and view function. Used when routing and building URLs. Defaults to view_func.__name__.

    • view_func (ft.RouteCallable | None) – The view function to associate with the endpoint name.

    • provide_automatic_options (bool | None) – Add the OPTIONS method and respond to OPTIONS requests automatically.

    • options (t.Any) – Extra options passed to the Rule object.

    Return type:

    None

• after_request(f)

  Register a function to run after each request to this object.

  The function is called with the response object, and must return a response object. This allows the functions to modify or replace the response before it is sent.

  If a function raises an exception, any remaining after_request functions will not be called. Therefore, this should not be used for actions that must execute, such as to close resources. Use teardown_request() for that.

  This is available on both app and blueprint objects. When used on an app, this executes after every request. When used on a blueprint, this executes after every request that the blueprint handles. To register with a blueprint and execute after every request, use Blueprint.after_app_request().

  • Parameters:

    f (T_after_request) –

    Return type:

    T_after_request

• after_request_funcs: dict[ft.AppOrBlueprintKey, list[ft.AfterRequestCallable[t.Any]]]

  A data structure of functions to call at the end of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the after_request() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• app_context()

  Create an AppContext. Use as a with block to push the context, which will make current_app point at this application.

  An application context is automatically pushed by RequestContext.push() when handling a request, and when running a CLI command. Use this to manually create a context outside of these situations.

  with app.app_context():
      init_db()

  See The Application Context.

  Changelog

  New in version 0.9.

  • Return type:

    AppContext

• app_ctx_globals_class

  alias of _AppCtxGlobals

• async_to_sync(func)

  Return a sync function that will run the coroutine function.

  result = app.async_to_sync(func)(*args, **kwargs)

  Override this method to change how the app converts async code to be synchronously callable.

  Changelog

  New in version 2.0.

  • Parameters:

    func (Callable[[…], Coroutine[Any, Any, Any]__]) –

    Return type:

    Callable[[…], Any]

• auto_find_instance_path()

  Tries to locate the instance path if it was not provided to the constructor of the application class. It will basically calculate the path to a folder named instance next to your main file or the package.

  Changelog

  New in version 0.8.

  • Return type:

    str

• before_request(f)

  Register a function to run before each request.

  For example, this can be used to open a database connection, or to load the logged in user from the session.

  @app.before_request
  def load_user():
      if "user_id" in session:
          g.user = db.session.get(session["user_id"])

  The function will be called without any arguments. If it returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.

  This is available on both app and blueprint objects. When used on an app, this executes before every request. When used on a blueprint, this executes before every request that the blueprint handles. To register with a blueprint and execute before every request, use Blueprint.before_app_request().

  • Parameters:

    f (T_before_request) –

    Return type:

    T_before_request

• before_request_funcs: dict[ft.AppOrBlueprintKey, list[ft.BeforeRequestCallable]]

  A data structure of functions to call at the beginning of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the before_request() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• blueprints: dict[str, Blueprint]

  Maps registered blueprint names to blueprint objects. The dict retains the order the blueprints were registered in. Blueprints can be registered multiple times, this dict does not track how often they were attached.

  Changelog

  New in version 0.7.

• cli: click.Group

  The Click command group for registering CLI commands for this object. The commands are available from the flask command once the application has been discovered and blueprints have been registered.

• config

  The configuration dictionary as Config. This behaves exactly like a regular dictionary but supports additional methods to load a config from files.

• config_class

  alias of Config

• context_processor(f)

  Registers a template context processor function. These functions run before rendering a template. The keys of the returned dict are added as variables available in the template.

  This is available on both app and blueprint objects. When used on an app, this is called for every rendered template. When used on a blueprint, this is called for templates rendered from the blueprint’s views. To register with a blueprint and affect every template, use Blueprint.app_context_processor().

  • Parameters:

    f (T_template_context_processor) –

    Return type:

    T_template_context_processor

• create_global_jinja_loader()

  Creates the loader for the Jinja2 environment. Can be used to override just the loader and keeping the rest unchanged. It’s discouraged to override this function. Instead one should override the jinja_loader() function instead.

  The global loader dispatches between the loaders of the application and the individual blueprints.

  Changelog

  New in version 0.7.

  • Return type:

    DispatchingJinjaLoader

• create_jinja_environment()

  Create the Jinja environment based on jinja_options and the various Jinja-related methods of the app. Changing jinja_options after this will have no effect. Also adds Flask-related globals and filters to the environment.

  Changelog

  Changed in version 0.11: Environment.auto_reload set in accordance with TEMPLATES_AUTO_RELOAD configuration option.

  New in version 0.5.

  • Return type:

    Environment

• create_url_adapter(request)

  Creates a URL adapter for the given request. The URL adapter is created at a point where the request context is not yet set up so the request is passed explicitly.

  Changelog

  Changed in version 1.0: SERVER_NAME no longer implicitly enables subdomain matching. Use subdomain_matching instead.

  Changed in version 0.9: This can now also be called without a request object when the URL adapter is created for the application context.

  New in version 0.6.

  • Parameters:

    request (Request | None) –

    Return type:

    MapAdapter | None

• property debug: bool

  Whether debug mode is enabled. When using flask run to start the development server, an interactive debugger will be shown for unhandled exceptions, and the server will be reloaded when code changes. This maps to the DEBUG config key. It may not behave as expected if set late.

  Do not enable debug mode when deploying in production.

  Default: False

• delete(rule, **options)

  Shortcut for route() with methods=["DELETE"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• dispatch_request()

  Does the request dispatching. Matches the URL and returns the return value of the view or error handler. This does not have to be a response object. In order to convert the return value to a proper response object, call make_response().

  Changelog

  Changed in version 0.7: This no longer does the exception handling, this code was moved to the new full_dispatch_request().

  • Return type:

    ft.ResponseReturnValue

• do_teardown_appcontext(exc=<object object>)

  Called right before the application context is popped.

  When handling a request, the application context is popped after the request context. See do_teardown_request().

  This calls all functions decorated with teardown_appcontext(). Then the appcontext_tearing_down signal is sent.

  This is called by AppContext.pop().

  Changelog

  New in version 0.9.

  • Parameters:

    exc (BaseException | None) –

    Return type:

    None

• do_teardown_request(exc=<object object>)

  Called after the request is dispatched and the response is returned, right before the request context is popped.

  This calls all functions decorated with teardown_request(), and Blueprint.teardown_request() if a blueprint handled the request. Finally, the request_tearing_down signal is sent.

  This is called by RequestContext.pop(), which may be delayed during testing to maintain access to resources.

  • Parameters:

    exc (BaseException | None) – An unhandled exception raised while dispatching the request. Detected from the current exception information if not passed. Passed to each teardown function.

    Return type:

    None

  Changelog

  Changed in version 0.9: Added the exc argument.

• endpoint(endpoint)

  Decorate a view function to register it for the given endpoint. Used if a rule is added without a view_func with add_url_rule().

  app.add_url_rule("/ex", endpoint="example")
  @app.endpoint("example")
  def example():
      ...

  • Parameters:

    endpoint (str) – The endpoint name to associate with the view function.

    Return type:

    Callable[[F], F]

• ensure_sync(func)

  Ensure that the function is synchronous for WSGI workers. Plain def functions are returned as-is. async def functions are wrapped to run and wait for the response.

  Override this method to change how the app runs async views.

  Changelog

  New in version 2.0.

  • Parameters:

    func (Callable[[…], Any]) –

    Return type:

    Callable[[…], Any]

• error_handler_spec: dict[ft.AppOrBlueprintKey, dict[int | None, dict[type[Exception], ft.ErrorHandlerCallable]]]

  A data structure of registered error handlers, in the format {scope: {code: {class: handler}}}. The scope key is the name of a blueprint the handlers are active for, or None for all requests. The code key is the HTTP status code for HTTPException, or None for other exceptions. The innermost dictionary maps exception classes to handler functions.

  To register an error handler, use the errorhandler() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• errorhandler(code_or_exception)

  Register a function to handle errors by code or exception class.

  A decorator that is used to register a function given an error code. Example:

  @app.errorhandler(404)
  def page_not_found(error):
      return 'This page does not exist', 404

  You can also register handlers for arbitrary exceptions:

  @app.errorhandler(DatabaseError)
  def special_exception_handler(error):
      return 'Database connection failed', 500

  This is available on both app and blueprint objects. When used on an app, this can handle errors from every request. When used on a blueprint, this can handle errors from requests that the blueprint handles. To register with a blueprint and affect every request, use Blueprint.app_errorhandler().

  Changelog

  New in version 0.7: Use register_error_handler() instead of modifying error_handler_spec directly, for application wide error handlers.

  New in version 0.7: One can now additionally also register custom exception types that do not necessarily have to be a subclass of the HTTPException class.

  • Parameters:

    code_or_exception (type[Exception] | int) – the code as integer for the handler, or an arbitrary exception

    Return type:

    Callable[[T_error_handler], T_error_handler]

• extensions: dict[str, t.Any]

  a place where extensions can store application specific state. For example this is where an extension could store database engines and similar things.

  The key must match the name of the extension module. For example in case of a “Flask-Foo” extension in flask_foo, the key would be 'foo'.

  Changelog

  New in version 0.7.

• full_dispatch_request()

  Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling.

  Changelog

  New in version 0.7.

  • Return type:

    Response

• get(rule, **options)

  Shortcut for route() with methods=["GET"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• get_send_file_max_age(filename)

  Used by send_file() to determine the max_age cache value for a given file path if it wasn’t passed.

  By default, this returns SEND_FILE_MAX_AGE_DEFAULT from the configuration of current_app. This defaults to None, which tells the browser to use conditional requests instead of a timed cache, which is usually preferable.

  Note this is a duplicate of the same method in the Flask class.

  Changelog

  Changed in version 2.0: The default configuration is None instead of 12 hours.

  New in version 0.9.

  • Parameters:

    filename (str | None) –

    Return type:

    int | None

• handle_exception(e)

  Handle an exception that did not have an error handler associated with it, or that was raised from an error handler. This always causes a 500 InternalServerError.

  Always sends the got_request_exception signal.

  If PROPAGATE_EXCEPTIONS is True, such as in debug mode, the error will be re-raised so that the debugger can display it. Otherwise, the original exception is logged, and an InternalServerError is returned.

  If an error handler is registered for InternalServerError or 500, it will be used. For consistency, the handler will always receive the InternalServerError. The original unhandled exception is available as e.original_exception.

  Changelog

  Changed in version 1.1.0: Always passes the InternalServerError instance to the handler, setting original_exception to the unhandled error.

  Changed in version 1.1.0: after_request functions and other finalization is done even for the default 500 response when there is no handler.

  New in version 0.3.

  • Parameters:

    e (Exception) –

    Return type:

    Response

• handle_http_exception(e)

  Handles an HTTP exception. By default this will invoke the registered error handlers and fall back to returning the exception as response.

  Changelog

  Changed in version 1.0.3: RoutingException, used internally for actions such as slash redirects during routing, is not passed to error handlers.

  Changed in version 1.0: Exceptions are looked up by code and by MRO, so HTTPException subclasses can be handled with a catch-all handler for the base HTTPException.

  New in version 0.3.

  • Parameters:

    e (HTTPException) –

    Return type:

    HTTPException | ft.ResponseReturnValue

• handle_url_build_error(error, endpoint, values)

  Called by url_for() if a BuildError was raised. If this returns a value, it will be returned by url_for, otherwise the error will be re-raised.

  Each function in url_build_error_handlers is called with error, endpoint and values. If a function returns None or raises a BuildError, it is skipped. Otherwise, its return value is returned by url_for.

  • Parameters:

    • error (BuildError) – The active BuildError being handled.

    • endpoint (str) – The endpoint being built.

    • values (dict[str, Any]) – The keyword arguments passed to url_for.

    Return type:

    str

• handle_user_exception(e)

  This method is called whenever an exception occurs that should be handled. A special case is HTTPException which is forwarded to the handle_http_exception() method. This function will either return a response value or reraise the exception with the same traceback.

  Changelog

  Changed in version 1.0: Key errors raised from request data like form show the bad key in debug mode rather than a generic bad request message.

  New in version 0.7.

  • Parameters:

    e (Exception) –

    Return type:

    HTTPException | ft.ResponseReturnValue

• property has_static_folder: bool

  True if static_folder is set.

  Changelog

  New in version 0.5.

• import_name

  The name of the package or module that this object belongs to. Do not change this once it is set by the constructor.

• inject_url_defaults(endpoint, values)

  Injects the URL defaults for the given endpoint directly into the values dictionary passed. This is used internally and automatically called on URL building.

  Changelog

  New in version 0.7.

  • Parameters:

    • endpoint (str) –

    • values (dict[str, Any]) –

    Return type:

    None

• instance_path

  Holds the path to the instance folder.

  Changelog

  New in version 0.8.

• iter_blueprints()

  Iterates over all blueprints by the order they were registered.

  Changelog

  New in version 0.11.

  • Return type:

    t.ValuesView[Blueprint]

• property jinja_env: Environment

  The Jinja environment used to load templates.

  The environment is created the first time this property is accessed. Changing jinja_options after that will have no effect.

• jinja_environment

  alias of Environment

• property jinja_loader: BaseLoader | None

  The Jinja loader for this object’s templates. By default this is a class jinja2.loaders.FileSystemLoader to template_folder if it is set.

  Changelog

  New in version 0.5.

• jinja_options: dict[str, t.Any] = {}

  Options that are passed to the Jinja environment in create_jinja_environment(). Changing these options after the environment is created (accessing jinja_env) will have no effect.

  Changelog

  Changed in version 1.1.0: This is a dict instead of an ImmutableDict to allow easier configuration.

• json: JSONProvider

  Provides access to JSON methods. Functions in flask.json will call methods on this provider when the application context is active. Used for handling JSON requests and responses.

  An instance of json_provider_class. Can be customized by changing that attribute on a subclass, or by assigning to this attribute afterwards.

  The default, DefaultJSONProvider, uses Python’s built-in json library. A different provider can use a different JSON library.

  Changelog

  New in version 2.2.

• json_provider_class

  alias of DefaultJSONProvider

• log_exception(exc_info)

  Logs an exception. This is called by handle_exception() if debugging is disabled and right before the handler is called. The default implementation logs the exception as error on the logger.

  Changelog

  New in version 0.8.

  • Parameters:

    exc_info (tuple[type, BaseException, TracebackType] | tuple[None, None__, None__]) –

    Return type:

    None

• property logger: Logger

  A standard Python Logger for the app, with the same name as name.

  In debug mode, the logger’s level will be set to DEBUG.

  If there are no handlers configured, a default handler will be added. See Logging for more information.

  Changelog

  Changed in version 1.1.0: The logger takes the same name as name rather than hard-coding "flask.app".

  Changed in version 1.0.0: Behavior was simplified. The logger is always named "flask.app". The level is only set during configuration, it doesn’t check app.debug each time. Only one format is used, not different ones depending on app.debug. No handlers are removed, and a handler is only added if no handlers are already configured.

  New in version 0.3.

• make_aborter()

  Create the object to assign to aborter. That object is called by flask.abort() to raise HTTP errors, and can be called directly as well.

  By default, this creates an instance of aborter_class, which defaults to werkzeug.exceptions.Aborter.

  Changelog

  New in version 2.2.

  • Return type:

    Aborter

• make_config(instance_relative=False)

  Used to create the config attribute by the Flask constructor. The instance_relative parameter is passed in from the constructor of Flask (there named instance_relative_config) and indicates if the config should be relative to the instance path or the root path of the application.

  Changelog

  New in version 0.8.

  • Parameters:

    instance_relative (bool) –

    Return type:

    Config

• make_default_options_response()

  This method is called to create the default OPTIONS response. This can be changed through subclassing to change the default behavior of OPTIONS responses.

  Changelog

  New in version 0.7.

  • Return type:

    Response

• make_response(rv)

  Convert the return value from a view function to an instance of response_class.

  • Parameters:

    rv (ft.ResponseReturnValue) –

    the return value from the view function. The view function must return a response. Returning None, or the view ending without returning, is not allowed. The following types are allowed for view_rv:

    str

    A response object is created with the string encoded to UTF-8 as the body.

    bytes

    A response object is created with the bytes as the body.

    dict

    A dictionary that will be jsonify’d before being returned.

    list

    A list that will be jsonify’d before being returned.

    generator or iterator

    A generator that returns str or bytes to be streamed as the response.

    tuple

    Either (body, status, headers), (body, status), or (body, headers), where body is any of the other types allowed here, status is a string or an integer, and headers is a dictionary or a list of (key, value) tuples. If body is a response_class instance, status overwrites the exiting value and headers are extended.

    response_class

    The object is returned unchanged.

    other Response class

    The object is coerced to response_class.

    callable()

    The function is called as a WSGI application. The result is used to create a response object.

    Return type:

    Response

  Changelog

  Changed in version 2.2: A generator will be converted to a streaming response. A list will be converted to a JSON response.

  Changed in version 1.1: A dict will be converted to a JSON response.

  Changed in version 0.9: Previously a tuple was interpreted as the arguments for the response object.

• make_shell_context()

  Returns the shell context for an interactive shell for this application. This runs all the registered shell context processors.

  Changelog

  New in version 0.11.

  • Return type:

    dict[str, Any]

• property name: str

  The name of the application. This is usually the import name with the difference that it’s guessed from the run file if the import name is main. This name is used as a display name when Flask needs the name of the application. It can be set and overridden to change the value.

  Changelog

  New in version 0.8.

• open_instance_resource(resource, mode=’rb’)

  Opens a resource from the application’s instance folder (instance_path). Otherwise works like open_resource(). Instance resources can also be opened for writing.

  • Parameters:

    • resource (str) – the name of the resource. To access resources within subfolders use forward slashes as separator.

    • mode (str) – resource file opening mode, default is ‘rb’.

    Return type:

    IO

• open_resource(resource, mode=’rb’)

  Open a resource file relative to root_path for reading.

  For example, if the file schema.sql is next to the file app.py where the Flask app is defined, it can be opened with:

  with app.open_resource("schema.sql") as f:
      conn.executescript(f.read())

  • Parameters:

    • resource (str) – Path to the resource relative to root_path.

    • mode (str) – Open the file in this mode. Only reading is supported, valid values are “r” (or “rt”) and “rb”.

    Return type:

    IO

  Note this is a duplicate of the same method in the Flask class.

• patch(rule, **options)

  Shortcut for route() with methods=["PATCH"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• permanent_session_lifetime

  A timedelta which is used to set the expiration date of a permanent session. The default is 31 days which makes a permanent session survive for roughly one month.

  This attribute can also be configured from the config with the PERMANENT_SESSION_LIFETIME configuration key. Defaults to timedelta(days=31)

• post(rule, **options)

  Shortcut for route() with methods=["POST"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• preprocess_request()

  Called before the request is dispatched. Calls url_value_preprocessors registered with the app and the current blueprint (if any). Then calls before_request_funcs registered with the app and the blueprint.

  If any before_request() handler returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.

  • Return type:

    ft.ResponseReturnValue | None

• process_response(response)

  Can be overridden in order to modify the response object before it’s sent to the WSGI server. By default this will call all the after_request() decorated functions.

  Changelog

  Changed in version 0.5: As of Flask 0.5 the functions registered for after request execution are called in reverse order of registration.

  • Parameters:

    response (Response) – a response_class object.

    Returns:

    a new response object or the same, has to be an instance of response_class.

    Return type:

    Response

• put(rule, **options)

  Shortcut for route() with methods=["PUT"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• redirect(location, code=302)

  Create a redirect response object.

  This is called by flask.redirect(), and can be called directly as well.

  • Parameters:

    • location (str) – The URL to redirect to.

    • code (int) – The status code for the redirect.

    Return type:

    BaseResponse

  Changelog

  New in version 2.2: Moved from flask.redirect, which calls this method.

• register_blueprint(blueprint, **options)

  Register a Blueprint on the application. Keyword arguments passed to this method will override the defaults set on the blueprint.

  Calls the blueprint’s register() method after recording the blueprint in the application’s blueprints.

  • Parameters:

    • blueprint (Blueprint) – The blueprint to register.

    • url_prefix – Blueprint routes will be prefixed with this.

    • subdomain – Blueprint routes will match on this subdomain.

    • url_defaults – Blueprint routes will use these default values for view arguments.

    • options (t.Any) – Additional keyword arguments are passed to BlueprintSetupState. They can be accessed in record() callbacks.

    Return type:

    None

  Changelog

  Changed in version 2.0.1: The name option can be used to change the (pre-dotted) name the blueprint is registered with. This allows the same blueprint to be registered multiple times with unique names for url_for.

  New in version 0.7.

• register_error_handler(code_or_exception, f)

  Alternative error attach function to the errorhandler() decorator that is more straightforward to use for non decorator usage.

  Changelog

  New in version 0.7.

  • Parameters:

    • code_or_exception (type[Exception] | int) –

    • f (ft.ErrorHandlerCallable) –

    Return type:

    None

• request_class

  alias of Request

• request_context(environ)

  Create a RequestContext representing a WSGI environment. Use a with block to push the context, which will make request point at this request.

  See The Request Context.

  Typically you should not call this from your own code. A request context is automatically pushed by the wsgi_app() when handling a request. Use test_request_context() to create an environment and context instead of this method.

  • Parameters:

    environ (WSGIEnvironment) – a WSGI environment

    Return type:

    RequestContext

• response_class

  alias of Response

• root_path

  Absolute path to the package on the filesystem. Used to look up resources contained in the package.

• route(rule, **options)

  Decorate a view function to register it with the given URL rule and options. Calls add_url_rule(), which has more details about the implementation.

  @app.route("/")
  def index():
      return "Hello, World!"

  See URL Route Registrations.

  The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed.

  The methods parameter defaults to ["GET"]. HEAD and OPTIONS are added automatically.

  • Parameters:

    • rule (str) – The URL rule string.

    • options (Any) – Extra options passed to the Rule object.

    Return type:

    Callable[[T_route], T_route]

• run(host=None, port=None, debug=None, load_dotenv=True, **options)

  Runs the application on a local development server.

  Do not use run() in a production setting. It is not intended to meet security and performance requirements for a production server. Instead, see Deploying to Production for WSGI server recommendations.

  If the debug flag is set the server will automatically reload for code changes and show a debugger in case an exception happened.

  If you want to run the application in debug mode, but disable the code execution on the interactive debugger, you can pass use_evalex=False as parameter. This will keep the debugger’s traceback screen active, but disable code execution.

  It is not recommended to use this function for development with automatic reloading as this is badly supported. Instead you should be using the flask command line script’s run support.

  Keep in Mind

  Flask will suppress any server error with a generic error page unless it is in debug mode. As such to enable just the interactive debugger without the code reloading, you have to invoke run() with debug=True and use_reloader=False. Setting use_debugger to True without being in debug mode won’t catch any exceptions because there won’t be any to catch.

  • Parameters:

    • host (str | None) – the hostname to listen on. Set this to '0.0.0.0' to have the server available externally as well. Defaults to '127.0.0.1' or the host in the SERVER_NAME config variable if present.

    • port (int | None) – the port of the webserver. Defaults to 5000 or the port defined in the SERVER_NAME config variable if present.

    • debug (bool | None) – if given, enable or disable debug mode. See debug.

    • load_dotenv (bool) – Load the nearest .env and .flaskenv files to set environment variables. Will also change the working directory to the directory containing the first file found.

    • options (Any) – the options to be forwarded to the underlying Werkzeug server. See werkzeug.serving.run_simple() for more information.

    Return type:

    None

  Changelog

  Changed in version 1.0: If installed, python-dotenv will be used to load environment variables from .env and .flaskenv files.

  The FLASK_DEBUG environment variable will override debug.

  Threaded mode is enabled by default.

  Changed in version 0.10: The default port is now picked from the SERVER_NAME variable.

• secret_key

  If a secret key is set, cryptographic components can use this to sign cookies and other things. Set this to a complex random value when you want to use the secure cookie for instance.

  This attribute can also be configured from the config with the SECRET_KEY configuration key. Defaults to None.

• select_jinja_autoescape(filename)

  Returns True if autoescaping should be active for the given template name. If no template name is given, returns True.

  Changelog

  Changed in version 2.2: Autoescaping is now enabled by default for .svg files.

  New in version 0.5.

  • Parameters:

    filename (str) –

    Return type:

    bool

• send_static_file(filename)

  The view function used to serve files from static_folder. A route is automatically registered for this view at static_url_path if static_folder is set.

  Note this is a duplicate of the same method in the Flask class.

  Changelog

  New in version 0.5.

  • Parameters:

    filename (str) –

    Return type:

    Response

• session_interface: SessionInterface = <flask.sessions.SecureCookieSessionInterface object>

  the session interface to use. By default an instance of SecureCookieSessionInterface is used here.

  Changelog

  New in version 0.8.

• shell_context_processor(f)

  Registers a shell context processor function.

  Changelog

  New in version 0.11.

  • Parameters:

    f (T_shell_context_processor) –

    Return type:

    T_shell_context_processor

• shell_context_processors: list[ft.ShellContextProcessorCallable]

  A list of shell context processor functions that should be run when a shell context is created.

  Changelog

  New in version 0.11.

• should_ignore_error(error)

  This is called to figure out if an error should be ignored or not as far as the teardown system is concerned. If this function returns True then the teardown handlers will not be passed the error.

  Changelog

  New in version 0.10.

  • Parameters:

    error (BaseException | None) –

    Return type:

    bool

• property static_folder: str | None

  The absolute path to the configured static folder. None if no static folder is set.

• property static_url_path: str | None

  The URL prefix that the static route will be accessible from.

  If it was not configured during init, it is derived from static_folder.

• teardown_appcontext(f)

  Registers a function to be called when the application context is popped. The application context is typically popped after the request context for each request, at the end of CLI commands, or after a manually pushed context ends.

  with app.app_context():
      ...

  When the with block exits (or ctx.pop() is called), the teardown functions are called just before the app context is made inactive. Since a request context typically also manages an application context it would also be called when you pop a request context.

  When a teardown function was called because of an unhandled exception it will be passed an error object. If an errorhandler() is registered, it will handle the exception and the teardown will not receive it.

  Teardown functions must avoid raising exceptions. If they execute code that might fail they must surround that code with a try/except block and log any errors.

  The return values of teardown functions are ignored.

  Changelog

  New in version 0.9.

  • Parameters:

    f (T_teardown) –

    Return type:

    T_teardown

• teardown_appcontext_funcs: list[ft.TeardownCallable]

  A list of functions that are called when the application context is destroyed. Since the application context is also torn down if the request ends this is the place to store code that disconnects from databases.

  Changelog

  New in version 0.9.

• teardown_request(f)

  Register a function to be called when the request context is popped. Typically this happens at the end of each request, but contexts may be pushed manually as well during testing.

  with app.test_request_context():
      ...

  When the with block exits (or ctx.pop() is called), the teardown functions are called just before the request context is made inactive.

  When a teardown function was called because of an unhandled exception it will be passed an error object. If an errorhandler() is registered, it will handle the exception and the teardown will not receive it.

  Teardown functions must avoid raising exceptions. If they execute code that might fail they must surround that code with a try/except block and log any errors.

  The return values of teardown functions are ignored.

  This is available on both app and blueprint objects. When used on an app, this executes after every request. When used on a blueprint, this executes after every request that the blueprint handles. To register with a blueprint and execute after every request, use Blueprint.teardown_app_request().

  • Parameters:

    f (T_teardown) –

    Return type:

    T_teardown

• teardown_request_funcs: dict[ft.AppOrBlueprintKey, list[ft.TeardownCallable]]

  A data structure of functions to call at the end of each request even if an exception is raised, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the teardown_request() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• template_context_processors: dict[ft.AppOrBlueprintKey, list[ft.TemplateContextProcessorCallable]]

  A data structure of functions to call to pass extra context values when rendering templates, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the context_processor() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• template_filter(name=None)

  A decorator that is used to register custom template filter. You can specify a name for the filter, otherwise the function name will be used. Example:

  @app.template_filter()
  def reverse(s):
      return s[::-1]

  • Parameters:

    name (str | None) – the optional name of the filter, otherwise the function name will be used.

    Return type:

    Callable[[T_template_filter], T_template_filter]

• template_folder

  The path to the templates folder, relative to root_path, to add to the template loader. None if templates should not be added.

• template_global(name=None)

  A decorator that is used to register a custom template global function. You can specify a name for the global function, otherwise the function name will be used. Example:

  @app.template_global()
  def double(n):
      return 2 * n

  Changelog

  New in version 0.10.

  • Parameters:

    name (str | None) – the optional name of the global function, otherwise the function name will be used.

    Return type:

    Callable[[T_template_global], T_template_global]

• template_test(name=None)

  A decorator that is used to register custom template test. You can specify a name for the test, otherwise the function name will be used. Example:

  @app.template_test()
  def is_prime(n):
      if n == 2:
          return True
      for i in range(2, int(math.ceil(math.sqrt(n))) + 1):
          if n % i == 0:
              return False
      return True

  Changelog

  New in version 0.10.

  • Parameters:

    name (str | None) – the optional name of the test, otherwise the function name will be used.

    Return type:

    Callable[[T_template_test], T_template_test]

• test_cli_runner(**kwargs)

  Create a CLI runner for testing CLI commands. See Running Commands with the CLI Runner.

  Returns an instance of test_cli_runner_class, by default FlaskCliRunner. The Flask app object is passed as the first argument.

  Changelog

  New in version 1.0.

  • Parameters:

    kwargs (t.Any) –

    Return type:

    FlaskCliRunner

• test_cli_runner_class: type[FlaskCliRunner] | None = None

  The CliRunner subclass, by default FlaskCliRunner that is used by test_cli_runner(). Its __init__ method should take a Flask app object as the first argument.

  Changelog

  New in version 1.0.

• test_client(use_cookies=True, **kwargs)

  Creates a test client for this application. For information about unit testing head over to Testing Flask Applications.

  Note that if you are testing for assertions or exceptions in your application code, you must set app.testing = True in order for the exceptions to propagate to the test client. Otherwise, the exception will be handled by the application (not visible to the test client) and the only indication of an AssertionError or other exception will be a 500 status code response to the test client. See the testing attribute. For example:

  app.testing = True
  client = app.test_client()

  The test client can be used in a with block to defer the closing down of the context until the end of the with block. This is useful if you want to access the context locals for testing:

  with app.test_client() as c:
      rv = c.get('/?vodka=42')
      assert request.args['vodka'] == '42'

  Additionally, you may pass optional keyword arguments that will then be passed to the application’s test_client_class constructor. For example:

  from flask.testing import FlaskClient
  class CustomClient(FlaskClient):
      def __init__(self, *args, **kwargs):
          self._authentication = kwargs.pop("authentication")
          super(CustomClient,self).__init__( *args, **kwargs)
  app.test_client_class = CustomClient
  client = app.test_client(authentication='Basic ....')

  See FlaskClient for more information.

  Changelog

  Changed in version 0.11: Added **kwargs to support passing additional keyword arguments to the constructor of test_client_class.

  New in version 0.7: The use_cookies parameter was added as well as the ability to override the client to be used by setting the test_client_class attribute.

  Changed in version 0.4: added support for with block usage for the client.

  • Parameters:

    • use_cookies (bool) –

    • kwargs (t.Any) –

    Return type:

    FlaskClient

• test_client_class: type[FlaskClient] | None = None

  The test_client() method creates an instance of this test client class. Defaults to FlaskClient.

  Changelog

  New in version 0.7.

• test_request_context(*args, **kwargs)

  Create a RequestContext for a WSGI environment created from the given values. This is mostly useful during testing, where you may want to run a function that uses request data without dispatching a full request.

  See The Request Context.

  Use a with block to push the context, which will make request point at the request for the created environment.

  with app.test_request_context(...):
      generate_report()

  When using the shell, it may be easier to push and pop the context manually to avoid indentation.

  ctx = app.test_request_context(...)
  ctx.push()
  ...
  ctx.pop()

  Takes the same arguments as Werkzeug’s EnvironBuilder, with some defaults from the application. See the linked Werkzeug docs for most of the available arguments. Flask-specific behavior is listed here.

  • Parameters:

    • path – URL path being requested.

    • base_url – Base URL where the app is being served, which path is relative to. If not given, built from PREFERRED_URL_SCHEME, subdomain, SERVER_NAME, and APPLICATION_ROOT.

    • subdomain – Subdomain name to append to SERVER_NAME.

    • url_scheme – Scheme to use instead of PREFERRED_URL_SCHEME.

    • data – The request body, either as a string or a dict of form keys and values.

    • json – If given, this is serialized as JSON and passed as data. Also defaults content_type to application/json.

    • args (Any) – other positional arguments passed to EnvironBuilder.

    • kwargs (Any) – other keyword arguments passed to EnvironBuilder.

    Return type:

    RequestContext

• testing

  The testing flag. Set this to True to enable the test mode of Flask extensions (and in the future probably also Flask itself). For example this might activate test helpers that have an additional runtime cost which should not be enabled by default.

  If this is enabled and PROPAGATE_EXCEPTIONS is not changed from the default it’s implicitly enabled.

  This attribute can also be configured from the config with the TESTING configuration key. Defaults to False.

• trap_http_exception(e)

  Checks if an HTTP exception should be trapped or not. By default this will return False for all exceptions except for a bad request key error if TRAP_BAD_REQUEST_ERRORS is set to True. It also returns True if TRAP_HTTP_EXCEPTIONS is set to True.

  This is called for all HTTP exceptions raised by a view function. If it returns True for any exception the error handler for this exception is not called and it shows up as regular exception in the traceback. This is helpful for debugging implicitly raised HTTP exceptions.

  Changelog

  Changed in version 1.0: Bad request errors are not trapped by default in debug mode.

  New in version 0.8.

  • Parameters:

    e (Exception) –

    Return type:

    bool

• update_template_context(context)

  Update the template context with some commonly used variables. This injects request, session, config and g into the template context as well as everything template context processors want to inject. Note that the as of Flask 0.6, the original values in the context will not be overridden if a context processor decides to return a value with the same key.

  • Parameters:

    context (dict[str, Any]) – the context as a dictionary that is updated in place to add extra variables.

    Return type:

    None

• url_build_error_handlers: list[t.Callable[[Exception, str, dict[str, t.Any]], str]]

  A list of functions that are called by handle_url_build_error() when url_for() raises a BuildError. Each function is called with error, endpoint and values. If a function returns None or raises a BuildError, it is skipped. Otherwise, its return value is returned by url_for.

  Changelog

  New in version 0.9.

• url_default_functions: dict[ft.AppOrBlueprintKey, list[ft.URLDefaultCallable]]

  A data structure of functions to call to modify the keyword arguments when generating URLs, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the url_defaults() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• url_defaults(f)

  Callback function for URL defaults for all view functions of the application. It’s called with the endpoint and values and should update the values passed in place.

  This is available on both app and blueprint objects. When used on an app, this is called for every request. When used on a blueprint, this is called for requests that the blueprint handles. To register with a blueprint and affect every request, use Blueprint.app_url_defaults().

  • Parameters:

    f (T_url_defaults) –

    Return type:

    T_url_defaults

• url_for(endpoint, *, _anchor=None, _method=None, _scheme=None, _external=None, **values)

  Generate a URL to the given endpoint with the given values.

  This is called by flask.url_for(), and can be called directly as well.

  An endpoint is the name of a URL rule, usually added with @app.route(), and usually the same name as the view function. A route defined in a Blueprint will prepend the blueprint’s name separated by a . to the endpoint.

  In some cases, such as email messages, you want URLs to include the scheme and domain, like https://example.com/hello. When not in an active request, URLs will be external by default, but this requires setting SERVER_NAME so Flask knows what domain to use. APPLICATION_ROOT and PREFERRED_URL_SCHEME should also be configured as needed. This config is only used when not in an active request.

  Functions can be decorated with url_defaults() to modify keyword arguments before the URL is built.

  If building fails for some reason, such as an unknown endpoint or incorrect values, the app’s handle_url_build_error() method is called. If that returns a string, that is returned, otherwise a BuildError is raised.

  • Parameters:

    • endpoint (str) – The endpoint name associated with the URL to generate. If this starts with a ., the current blueprint name (if any) will be used.

    • _anchor (str | None) – If given, append this as #anchor to the URL.

    • _method (str | None) – If given, generate the URL associated with this method for the endpoint.

    • _scheme (str | None) – If given, the URL will have this scheme if it is external.

    • _external (bool | None) – If given, prefer the URL to be internal (False) or require it to be external (True). External URLs include the scheme and domain. When not in an active request, URLs are external by default.

    • values (Any) – Values to use for the variable parts of the URL rule. Unknown keys are appended as query string arguments, like ?a=b&c=d.

    Return type:

    str

  Changelog

  New in version 2.2: Moved from flask.url_for, which calls this method.

• url_map

  The Map for this instance. You can use this to change the routing converters after the class was created but before any routes are connected. Example:

  from werkzeug.routing import BaseConverter
  class ListConverter(BaseConverter):
      def to_python(self, value):
          return value.split(',')
      def to_url(self, values):
          return ','.join(super(ListConverter, self).to_url(value)
                          for value in values)
  app = Flask(__name__)
  app.url_map.converters['list'] = ListConverter

• url_map_class

  alias of Map

• url_rule_class

  alias of Rule

• url_value_preprocessor(f)

  Register a URL value preprocessor function for all view functions in the application. These functions will be called before the before_request() functions.

  The function can modify the values captured from the matched url before they are passed to the view. For example, this can be used to pop a common language code value and place it in g rather than pass it to every view.

  The function is passed the endpoint name and values dict. The return value is ignored.

  This is available on both app and blueprint objects. When used on an app, this is called for every request. When used on a blueprint, this is called for requests that the blueprint handles. To register with a blueprint and affect every request, use Blueprint.app_url_value_preprocessor().

  • Parameters:

    f (T_url_value_preprocessor) –

    Return type:

    T_url_value_preprocessor

• url_value_preprocessors: dict[ft.AppOrBlueprintKey, list[ft.URLValuePreprocessorCallable]]

  A data structure of functions to call to modify the keyword arguments passed to the view function, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the url_value_preprocessor() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• view_functions: dict[str, ft.RouteCallable]

  A dictionary mapping endpoint names to view functions.

  To register a view function, use the route() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• wsgi_app(environ, start_response)

  The actual WSGI application. This is not implemented in __call__() so that middlewares can be applied without losing a reference to the app object. Instead of doing this:

  app = MyMiddleware(app)

  It’s a better idea to do this instead:

  app.wsgi_app = MyMiddleware(app.wsgi_app)

  Then you still have the original application object around and can continue to call methods on it.

  Changelog

  Changed in version 0.7: Teardown events for the request and app contexts are called even if an unhandled error occurs. Other events may not be called depending on when an error occurs during dispatch. See Callbacks and Errors.

  • Parameters:

    • environ (WSGIEnvironment) – A WSGI environment.

    • start_response (StartResponse) – A callable accepting a status code, a list of headers, and an optional exception context to start the response.

    Return type:

    cabc.Iterable[bytes]

Blueprint Objects

class flask.Blueprint(name, import_name, static_folder=None, static_url_path=None, template_folder=None, url_prefix=None, subdomain=None, url_defaults=None, root_path=None, cli_group=<object object>)

• Parameters:

  • name (str) –

  • import_name (str) –

  • static_folder (str | os.PathLike[str] | None) –

  • static_url_path (str | None) –

  • template_folder (str | os.PathLike[str] | None) –

  • url_prefix (str | None) –

  • subdomain (str | None) –

  • url_defaults (dict[str, t.Any__] | None) –

  • root_path (str | None) –

  • cli_group (str | None) –

• add_app_template_filter(f, name=None)

  Register a template filter, available in any template rendered by the application. Works like the app_template_filter() decorator. Equivalent to Flask.add_template_filter().

  • Parameters:

    • name (str | None) – the optional name of the filter, otherwise the function name will be used.

    • f (Callable[[…], Any]) –

    Return type:

    None

• add_app_template_global(f, name=None)

  Register a template global, available in any template rendered by the application. Works like the app_template_global() decorator. Equivalent to Flask.add_template_global().

  Changelog

  New in version 0.10.

  • Parameters:

    • name (str | None) – the optional name of the global, otherwise the function name will be used.

    • f (Callable[[…], Any]) –

    Return type:

    None

• add_app_template_test(f, name=None)

  Register a template test, available in any template rendered by the application. Works like the app_template_test() decorator. Equivalent to Flask.add_template_test().

  Changelog

  New in version 0.10.

  • Parameters:

    • name (str | None) – the optional name of the test, otherwise the function name will be used.

    • f (Callable[[…], bool]) –

    Return type:

    None

• add_url_rule(rule, endpoint=None, view_func=None, provide_automatic_options=None, **options)

  Register a URL rule with the blueprint. See Flask.add_url_rule() for full documentation.

  The URL rule is prefixed with the blueprint’s URL prefix. The endpoint name, used with url_for(), is prefixed with the blueprint’s name.

  • Parameters:

    • rule (str) –

    • endpoint (str | None) –

    • view_func (ft.RouteCallable | None) –

    • provide_automatic_options (bool | None) –

    • options (t.Any) –

    Return type:

    None

• after_app_request(f)

  Like after_request(), but after every request, not only those handled by the blueprint. Equivalent to Flask.after_request().

  • Parameters:

    f (T_after_request) –

    Return type:

    T_after_request

• after_request(f)

  Register a function to run after each request to this object.

  The function is called with the response object, and must return a response object. This allows the functions to modify or replace the response before it is sent.

  If a function raises an exception, any remaining after_request functions will not be called. Therefore, this should not be used for actions that must execute, such as to close resources. Use teardown_request() for that.

  This is available on both app and blueprint objects. When used on an app, this executes after every request. When used on a blueprint, this executes after every request that the blueprint handles. To register with a blueprint and execute after every request, use Blueprint.after_app_request().

  • Parameters:

    f (T_after_request) –

    Return type:

    T_after_request

• after_request_funcs: dict[ft.AppOrBlueprintKey, list[ft.AfterRequestCallable[t.Any]]]

  A data structure of functions to call at the end of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the after_request() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• app_context_processor(f)

  Like context_processor(), but for templates rendered by every view, not only by the blueprint. Equivalent to Flask.context_processor().

  • Parameters:

    f (T_template_context_processor) –

    Return type:

    T_template_context_processor

• app_errorhandler(code)

  Like errorhandler(), but for every request, not only those handled by the blueprint. Equivalent to Flask.errorhandler().

  • Parameters:

    code (type[Exception] | int) –

    Return type:

    Callable[[T_error_handler], T_error_handler]

• app_template_filter(name=None)

  Register a template filter, available in any template rendered by the application. Equivalent to Flask.template_filter().

  • Parameters:

    name (str | None) – the optional name of the filter, otherwise the function name will be used.

    Return type:

    Callable[[T_template_filter], T_template_filter]

• app_template_global(name=None)

  Register a template global, available in any template rendered by the application. Equivalent to Flask.template_global().

  Changelog

  New in version 0.10.

  • Parameters:

    name (str | None) – the optional name of the global, otherwise the function name will be used.

    Return type:

    Callable[[T_template_global], T_template_global]

• app_template_test(name=None)

  Register a template test, available in any template rendered by the application. Equivalent to Flask.template_test().

  Changelog

  New in version 0.10.

  • Parameters:

    name (str | None) – the optional name of the test, otherwise the function name will be used.

    Return type:

    Callable[[T_template_test], T_template_test]

• app_url_defaults(f)

  Like url_defaults(), but for every request, not only those handled by the blueprint. Equivalent to Flask.url_defaults().

  • Parameters:

    f (T_url_defaults) –

    Return type:

    T_url_defaults

• app_url_value_preprocessor(f)

  Like url_value_preprocessor(), but for every request, not only those handled by the blueprint. Equivalent to Flask.url_value_preprocessor().

  • Parameters:

    f (T_url_value_preprocessor) –

    Return type:

    T_url_value_preprocessor

• before_app_request(f)

  Like before_request(), but before every request, not only those handled by the blueprint. Equivalent to Flask.before_request().

  • Parameters:

    f (T_before_request) –

    Return type:

    T_before_request

• before_request(f)

  Register a function to run before each request.

  For example, this can be used to open a database connection, or to load the logged in user from the session.

  @app.before_request
  def load_user():
      if "user_id" in session:
          g.user = db.session.get(session["user_id"])

  The function will be called without any arguments. If it returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.

  This is available on both app and blueprint objects. When used on an app, this executes before every request. When used on a blueprint, this executes before every request that the blueprint handles. To register with a blueprint and execute before every request, use Blueprint.before_app_request().

  • Parameters:

    f (T_before_request) –

    Return type:

    T_before_request

• before_request_funcs: dict[ft.AppOrBlueprintKey, list[ft.BeforeRequestCallable]]

  A data structure of functions to call at the beginning of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the before_request() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• cli: click.Group

  The Click command group for registering CLI commands for this object. The commands are available from the flask command once the application has been discovered and blueprints have been registered.

• context_processor(f)

  Registers a template context processor function. These functions run before rendering a template. The keys of the returned dict are added as variables available in the template.

  This is available on both app and blueprint objects. When used on an app, this is called for every rendered template. When used on a blueprint, this is called for templates rendered from the blueprint’s views. To register with a blueprint and affect every template, use Blueprint.app_context_processor().

  • Parameters:

    f (T_template_context_processor) –

    Return type:

    T_template_context_processor

• delete(rule, **options)

  Shortcut for route() with methods=["DELETE"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• endpoint(endpoint)

  Decorate a view function to register it for the given endpoint. Used if a rule is added without a view_func with add_url_rule().

  app.add_url_rule("/ex", endpoint="example")
  @app.endpoint("example")
  def example():
      ...

  • Parameters:

    endpoint (str) – The endpoint name to associate with the view function.

    Return type:

    Callable[[F], F]

• error_handler_spec: dict[ft.AppOrBlueprintKey, dict[int | None, dict[type[Exception], ft.ErrorHandlerCallable]]]

  A data structure of registered error handlers, in the format {scope: {code: {class: handler}}}. The scope key is the name of a blueprint the handlers are active for, or None for all requests. The code key is the HTTP status code for HTTPException, or None for other exceptions. The innermost dictionary maps exception classes to handler functions.

  To register an error handler, use the errorhandler() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• errorhandler(code_or_exception)

  Register a function to handle errors by code or exception class.

  A decorator that is used to register a function given an error code. Example:

  @app.errorhandler(404)
  def page_not_found(error):
      return 'This page does not exist', 404

  You can also register handlers for arbitrary exceptions:

  @app.errorhandler(DatabaseError)
  def special_exception_handler(error):
      return 'Database connection failed', 500

  This is available on both app and blueprint objects. When used on an app, this can handle errors from every request. When used on a blueprint, this can handle errors from requests that the blueprint handles. To register with a blueprint and affect every request, use Blueprint.app_errorhandler().

  Changelog

  New in version 0.7: Use register_error_handler() instead of modifying error_handler_spec directly, for application wide error handlers.

  New in version 0.7: One can now additionally also register custom exception types that do not necessarily have to be a subclass of the HTTPException class.

  • Parameters:

    code_or_exception (type[Exception] | int) – the code as integer for the handler, or an arbitrary exception

    Return type:

    Callable[[T_error_handler], T_error_handler]

• get(rule, **options)

  Shortcut for route() with methods=["GET"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• get_send_file_max_age(filename)

  Used by send_file() to determine the max_age cache value for a given file path if it wasn’t passed.

  By default, this returns SEND_FILE_MAX_AGE_DEFAULT from the configuration of current_app. This defaults to None, which tells the browser to use conditional requests instead of a timed cache, which is usually preferable.

  Note this is a duplicate of the same method in the Flask class.

  Changelog

  Changed in version 2.0: The default configuration is None instead of 12 hours.

  New in version 0.9.

  • Parameters:

    filename (str | None) –

    Return type:

    int | None

• property has_static_folder: bool

  True if static_folder is set.

  Changelog

  New in version 0.5.

• import_name

  The name of the package or module that this object belongs to. Do not change this once it is set by the constructor.

• property jinja_loader: BaseLoader | None

  The Jinja loader for this object’s templates. By default this is a class jinja2.loaders.FileSystemLoader to template_folder if it is set.

  Changelog

  New in version 0.5.

• make_setup_state(app, options, first_registration=False)

  Creates an instance of BlueprintSetupState() object that is later passed to the register callback functions. Subclasses can override this to return a subclass of the setup state.

  • Parameters:

    • app (App) –

    • options (dict[str, t.Any__]) –

    • first_registration (bool) –

    Return type:

    BlueprintSetupState

• open_resource(resource, mode=’rb’)

  Open a resource file relative to root_path for reading.

  For example, if the file schema.sql is next to the file app.py where the Flask app is defined, it can be opened with:

  with app.open_resource("schema.sql") as f:
      conn.executescript(f.read())

  • Parameters:

    • resource (str) – Path to the resource relative to root_path.

    • mode (str) – Open the file in this mode. Only reading is supported, valid values are “r” (or “rt”) and “rb”.

    Return type:

    IO

  Note this is a duplicate of the same method in the Flask class.

• patch(rule, **options)

  Shortcut for route() with methods=["PATCH"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• post(rule, **options)

  Shortcut for route() with methods=["POST"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• put(rule, **options)

  Shortcut for route() with methods=["PUT"].

  Changelog

  New in version 2.0.

  • Parameters:

    • rule (str) –

    • options (Any) –

    Return type:

    Callable[[T_route], T_route]

• record(func)

  Registers a function that is called when the blueprint is registered on the application. This function is called with the state as argument as returned by the make_setup_state() method.

  • Parameters:

    func (Callable[__[BlueprintSetupState]__, None__]) –

    Return type:

    None

• record_once(func)

  Works like record() but wraps the function in another function that will ensure the function is only called once. If the blueprint is registered a second time on the application, the function passed is not called.

  • Parameters:

    func (Callable[__[BlueprintSetupState]__, None__]) –

    Return type:

    None

• register(app, options)

  Called by Flask.register_blueprint() to register all views and callbacks registered on the blueprint with the application. Creates a BlueprintSetupState and calls each record() callback with it.

  • Parameters:

    • app (App) – The application this blueprint is being registered with.

    • options (dict[str, t.Any__]) – Keyword arguments forwarded from register_blueprint().

    Return type:

    None

  Changelog

  Changed in version 2.3: Nested blueprints now correctly apply subdomains.

  Changed in version 2.1: Registering the same blueprint with the same name multiple times is an error.

  Changed in version 2.0.1: Nested blueprints are registered with their dotted name. This allows different blueprints with the same name to be nested at different locations.

  Changed in version 2.0.1: The name option can be used to change the (pre-dotted) name the blueprint is registered with. This allows the same blueprint to be registered multiple times with unique names for url_for.

• register_blueprint(blueprint, **options)

  Register a Blueprint on this blueprint. Keyword arguments passed to this method will override the defaults set on the blueprint.

  Changelog

  Changed in version 2.0.1: The name option can be used to change the (pre-dotted) name the blueprint is registered with. This allows the same blueprint to be registered multiple times with unique names for url_for.

  New in version 2.0.

  • Parameters:

    • blueprint (Blueprint) –

    • options (Any) –

    Return type:

    None

• register_error_handler(code_or_exception, f)

  Alternative error attach function to the errorhandler() decorator that is more straightforward to use for non decorator usage.

  Changelog

  New in version 0.7.

  • Parameters:

    • code_or_exception (type[Exception] | int) –

    • f (ft.ErrorHandlerCallable) –

    Return type:

    None

• root_path

  Absolute path to the package on the filesystem. Used to look up resources contained in the package.

• route(rule, **options)

  Decorate a view function to register it with the given URL rule and options. Calls add_url_rule(), which has more details about the implementation.

  @app.route("/")
  def index():
      return "Hello, World!"

  See URL Route Registrations.

  The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed.

  The methods parameter defaults to ["GET"]. HEAD and OPTIONS are added automatically.

  • Parameters:

    • rule (str) – The URL rule string.

    • options (Any) – Extra options passed to the Rule object.

    Return type:

    Callable[[T_route], T_route]

• send_static_file(filename)

  The view function used to serve files from static_folder. A route is automatically registered for this view at static_url_path if static_folder is set.

  Note this is a duplicate of the same method in the Flask class.

  Changelog

  New in version 0.5.

  • Parameters:

    filename (str) –

    Return type:

    Response

• property static_folder: str | None

  The absolute path to the configured static folder. None if no static folder is set.

• property static_url_path: str | None

  The URL prefix that the static route will be accessible from.

  If it was not configured during init, it is derived from static_folder.

• teardown_app_request(f)

  Like teardown_request(), but after every request, not only those handled by the blueprint. Equivalent to Flask.teardown_request().

  • Parameters:

    f (T_teardown) –

    Return type:

    T_teardown

• teardown_request(f)

  Register a function to be called when the request context is popped. Typically this happens at the end of each request, but contexts may be pushed manually as well during testing.

  with app.test_request_context():
      ...

  When the with block exits (or ctx.pop() is called), the teardown functions are called just before the request context is made inactive.

  When a teardown function was called because of an unhandled exception it will be passed an error object. If an errorhandler() is registered, it will handle the exception and the teardown will not receive it.

  Teardown functions must avoid raising exceptions. If they execute code that might fail they must surround that code with a try/except block and log any errors.

  The return values of teardown functions are ignored.

  This is available on both app and blueprint objects. When used on an app, this executes after every request. When used on a blueprint, this executes after every request that the blueprint handles. To register with a blueprint and execute after every request, use Blueprint.teardown_app_request().

  • Parameters:

    f (T_teardown) –

    Return type:

    T_teardown

• teardown_request_funcs: dict[ft.AppOrBlueprintKey, list[ft.TeardownCallable]]

  A data structure of functions to call at the end of each request even if an exception is raised, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the teardown_request() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• template_context_processors: dict[ft.AppOrBlueprintKey, list[ft.TemplateContextProcessorCallable]]

  A data structure of functions to call to pass extra context values when rendering templates, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the context_processor() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• template_folder

  The path to the templates folder, relative to root_path, to add to the template loader. None if templates should not be added.

• url_default_functions: dict[ft.AppOrBlueprintKey, list[ft.URLDefaultCallable]]

  A data structure of functions to call to modify the keyword arguments when generating URLs, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the url_defaults() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• url_defaults(f)

  Callback function for URL defaults for all view functions of the application. It’s called with the endpoint and values and should update the values passed in place.

  This is available on both app and blueprint objects. When used on an app, this is called for every request. When used on a blueprint, this is called for requests that the blueprint handles. To register with a blueprint and affect every request, use Blueprint.app_url_defaults().

  • Parameters:

    f (T_url_defaults) –

    Return type:

    T_url_defaults

• url_value_preprocessor(f)

  Register a URL value preprocessor function for all view functions in the application. These functions will be called before the before_request() functions.

  The function can modify the values captured from the matched url before they are passed to the view. For example, this can be used to pop a common language code value and place it in g rather than pass it to every view.

  The function is passed the endpoint name and values dict. The return value is ignored.

  This is available on both app and blueprint objects. When used on an app, this is called for every request. When used on a blueprint, this is called for requests that the blueprint handles. To register with a blueprint and affect every request, use Blueprint.app_url_value_preprocessor().

  • Parameters:

    f (T_url_value_preprocessor) –

    Return type:

    T_url_value_preprocessor

• url_value_preprocessors: dict[ft.AppOrBlueprintKey, list[ft.URLValuePreprocessorCallable]]

  A data structure of functions to call to modify the keyword arguments passed to the view function, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

  To register a function, use the url_value_preprocessor() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

• view_functions: dict[str, ft.RouteCallable]

  A dictionary mapping endpoint names to view functions.

  To register a view function, use the route() decorator.

  This data structure is internal. It should not be modified directly and its format may change at any time.

Incoming Request Data

class flask.Request(environ, populate_request=True, shallow=False)

The request object used by default in Flask. Remembers the matched endpoint and view arguments.

It is what ends up as request. If you want to replace the request object used you can subclass this and set request_class to your subclass.

The request object is a Request subclass and provides all of the attributes Werkzeug defines plus a few Flask specific ones.

• Parameters:

  • environ (WSGIEnvironment) –

  • populate_request (bool) –

  • shallow (bool) –

• property accept_charsets: CharsetAccept

  List of charsets this client supports as CharsetAccept object.

• property accept_encodings: Accept

  List of encodings this client accepts. Encodings in a HTTP term are compression encodings such as gzip. For charsets have a look at accept_charset.

• property accept_languages: LanguageAccept

  List of languages this client accepts as LanguageAccept object.

• property accept_mimetypes: MIMEAccept

  List of mimetypes this client supports as MIMEAccept object.

• access_control_request_headers

  Sent with a preflight request to indicate which headers will be sent with the cross origin request. Set access_control_allow_headers on the response to indicate which headers are allowed.

• access_control_request_method

  Sent with a preflight request to indicate which method will be used for the cross origin request. Set access_control_allow_methods on the response to indicate which methods are allowed.

• property access_route: list[str]

  If a forwarded header exists this is a list of all ip addresses from the client ip to the last proxy server.

• classmethod application(f)

  Decorate a function as responder that accepts the request as the last argument. This works like the responder() decorator but the function is passed the request object as the last argument and the request object will be closed automatically:

  @Request.application
  def my_wsgi_app(request):
      return Response('Hello World!')

  As of Werkzeug 0.14 HTTP exceptions are automatically caught and converted to responses instead of failing.

  • Parameters:

    f (t.Callable[[Request]__, WSGIApplication__]) – the WSGI callable to decorate

    Returns:

    a new WSGI callable

    Return type:

    WSGIApplication

• property args: MultiDict[str, str]

  The parsed URL parameters (the part in the URL after the question mark).

  By default an ImmutableMultiDict is returned from this function. This can be changed by setting parameter_storage_class to a different type. This might be necessary if the order of the form data is important.

  Changelog

  Changed in version 2.3: Invalid bytes remain percent encoded.

• property authorization: Authorization | None

  The Authorization header parsed into an Authorization object. None if the header is not present.

  Changelog

  Changed in version 2.3: Authorization is no longer a dict. The token attribute was added for auth schemes that use a token instead of parameters.

• property base_url: str

  Like url but without the query string.

• property blueprint: str | None

  The registered name of the current blueprint.

  This will be None if the endpoint is not part of a blueprint, or if URL matching failed or has not been performed yet.

  This does not necessarily match the name the blueprint was created with. It may have been nested, or registered with a different name.

• property blueprints: list[str]

  The registered names of the current blueprint upwards through parent blueprints.

  This will be an empty list if there is no current blueprint, or if URL matching failed.

  Changelog

  New in version 2.0.1.

• property cache_control: RequestCacheControl

  A RequestCacheControl object for the incoming cache control headers.

• close()

  Closes associated resources of this request object. This closes all file handles explicitly. You can also use the request object in a with statement which will automatically close it.

  Changelog

  New in version 0.9.

  • Return type:

    None

• content_encoding

  The Content-Encoding entity-header field is used as a modifier to the media-type. When present, its value indicates what additional content codings have been applied to the entity-body, and thus what decoding mechanisms must be applied in order to obtain the media-type referenced by the Content-Type header field.

  Changelog

  New in version 0.9.

• property content_length: int | None

  The Content-Length entity-header field indicates the size of the entity-body in bytes or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.

• content_md5

  The Content-MD5 entity-header field, as defined in RFC 1864, is an MD5 digest of the entity-body for the purpose of providing an end-to-end message integrity check (MIC) of the entity-body. (Note: a MIC is good for detecting accidental modification of the entity-body in transit, but is not proof against malicious attacks.)

  Changelog

  New in version 0.9.

• content_type

  The Content-Type entity-header field indicates the media type of the entity-body sent to the recipient or, in the case of the HEAD method, the media type that would have been sent had the request been a GET.

• property cookies: ImmutableMultiDict[str, str]

  A dict with the contents of all cookies transmitted with the request.

• property data: bytes

  The raw data read from stream. Will be empty if the request represents form data.

  To get the raw data even if it represents form data, use get_data().

• date

  The Date general-header field represents the date and time at which the message was originated, having the same semantics as orig-date in RFC 822.

  Changelog

  Changed in version 2.0: The datetime object is timezone-aware.

• dict_storage_class

  alias of ImmutableMultiDict

• property endpoint: str | None

  The endpoint that matched the request URL.

  This will be None if matching failed or has not been performed yet.

  This in combination with view_args can be used to reconstruct the same URL or a modified URL.

• environ: WSGIEnvironment

  The WSGI environment containing HTTP headers and information from the WSGI server.

• property files: ImmutableMultiDict[str, FileStorage]

  MultiDict object containing all uploaded files. Each key in files is the name from the <input type="file" name="">. Each value in files is a Werkzeug FileStorage object.

  It basically behaves like a standard file object you know from Python, with the difference that it also has a save() function that can store the file on the filesystem.

  Note that files will only contain data if the request method was POST, PUT or PATCH and the <form> that posted to the request had enctype="multipart/form-data". It will be empty otherwise.

  See the MultiDict / FileStorage documentation for more details about the used data structure.

• property form: ImmutableMultiDict[str, str]

  The form parameters. By default an ImmutableMultiDict is returned from this function. This can be changed by setting parameter_storage_class to a different type. This might be necessary if the order of the form data is important.

  Please keep in mind that file uploads will not end up here, but instead in the files attribute.

  Changelog

  Changed in version 0.9: Previous to Werkzeug 0.9 this would only contain form data for POST and PUT requests.

• form_data_parser_class

  alias of FormDataParser

• classmethod from_values(*args, **kwargs)

  Create a new request object based on the values provided. If environ is given missing values are filled from there. This method is useful for small scripts when you need to simulate a request from an URL. Do not use this method for unittesting, there is a full featured client object (Client) that allows to create multipart requests, support for cookies etc.

  This accepts the same options as the EnvironBuilder.

  Changelog

  Changed in version 0.5: This method now accepts the same arguments as EnvironBuilder. Because of this the environ parameter is now called environ_overrides.

  • Returns:

    request object

    Parameters:

    • args (Any) –

    • kwargs (Any) –

    Return type:

    Request

• property full_path: str

  Requested path, including the query string.

• get_data(cache=True, as_text=False, parse_form_data=False)

  This reads the buffered incoming data from the client into one bytes object. By default this is cached but that behavior can be changed by setting cache to False.

  Usually it’s a bad idea to call this method without checking the content length first as a client could send dozens of megabytes or more to cause memory problems on the server.

  Note that if the form data was already parsed this method will not return anything as form data parsing does not cache the data like this method does. To implicitly invoke form data parsing function set parse_form_data to True. When this is done the return value of this method will be an empty string if the form parser handles the data. This generally is not necessary as if the whole data is cached (which is the default) the form parser will used the cached data to parse the form data. Please be generally aware of checking the content length first in any case before calling this method to avoid exhausting server memory.

  If as_text is set to True the return value will be a decoded string.

  Changelog

  New in version 0.9.

  • Parameters:

    • cache (bool) –

    • as_text (bool) –

    • parse_form_data (bool) –

    Return type:

    bytes | str

• get_json(force=False, silent=False, cache=True)

  Parse data as JSON.

  If the mimetype does not indicate JSON (application/json, see is_json), or parsing fails, on_json_loading_failed() is called and its return value is used as the return value. By default this raises a 415 Unsupported Media Type resp.

  • Parameters:

    • force (bool) – Ignore the mimetype and always try to parse JSON.

    • silent (bool) – Silence mimetype and parsing errors, and return None instead.

    • cache (bool) – Store the parsed JSON to return for subsequent calls.

    Return type:

    Any | None

  Changelog

  Changed in version 2.3: Raise a 415 error instead of 400.

  Changed in version 2.1: Raise a 400 error if the content type is incorrect.

• headers

  The headers received with the request.

• property host: str

  The host name the request was made to, including the port if it’s non-standard. Validated with trusted_hosts.

• property host_url: str

  The request URL scheme and host only.

• property if_match: ETags

  An object containing all the etags in the If-Match header.

  • Return type:

    ETags

• property if_modified_since: datetime | None

  The parsed If-Modified-Since header as a datetime object.

  Changelog

  Changed in version 2.0: The datetime object is timezone-aware.

• property if_none_match: ETags

  An object containing all the etags in the If-None-Match header.

  • Return type:

    ETags

• property if_range: IfRange

  The parsed If-Range header.

  Changelog

  Changed in version 2.0: IfRange.date is timezone-aware.

  New in version 0.7.

• property if_unmodified_since: datetime | None

  The parsed If-Unmodified-Since header as a datetime object.

  Changelog

  Changed in version 2.0: The datetime object is timezone-aware.

• input_stream

  The raw WSGI input stream, without any safety checks.

  This is dangerous to use. It does not guard against infinite streams or reading past content_length or max_content_length.

  Use stream instead.

• property is_json: bool

  Check if the mimetype indicates JSON data, either application/json or application/*+json.

• is_multiprocess

  boolean that is True if the application is served by a WSGI server that spawns multiple processes.

• is_multithread

  boolean that is True if the application is served by a multithreaded WSGI server.

• is_run_once

  boolean that is True if the application will be executed only once in a process lifetime. This is the case for CGI for example, but it’s not guaranteed that the execution only happens one time.

• property is_secure: bool

  True if the request was made with a secure protocol (HTTPS or WSS).

• property json: Any | None

  The parsed JSON data if mimetype indicates JSON (application/json, see is_json).

  Calls get_json() with default arguments.

  If the request content type is not application/json, this will raise a 415 Unsupported Media Type error.

  Changelog

  Changed in version 2.3: Raise a 415 error instead of 400.

  Changed in version 2.1: Raise a 400 error if the content type is incorrect.

• list_storage_class

  alias of ImmutableList

• make_form_data_parser()

  Creates the form data parser. Instantiates the form_data_parser_class with some parameters.

  Changelog

  New in version 0.8.

  • Return type:

    FormDataParser

• property max_content_length: int | None

  Read-only view of the MAX_CONTENT_LENGTH config key.

• max_form_memory_size: int | None = None

  the maximum form field size. This is forwarded to the form data parsing function (parse_form_data()). When set and the form or files attribute is accessed and the data in memory for post data is longer than the specified value a RequestEntityTooLarge exception is raised.

  Changelog

  New in version 0.5.

• max_form_parts = 1000

  The maximum number of multipart parts to parse, passed to form_data_parser_class. Parsing form data with more than this many parts will raise RequestEntityTooLarge.

  Changelog

  New in version 2.2.3.

• max_forwards

  The Max-Forwards request-header field provides a mechanism with the TRACE and OPTIONS methods to limit the number of proxies or gateways that can forward the request to the next inbound server.

• method

  The method the request was made with, such as GET.

• property mimetype: str

  Like content_type, but without parameters (eg, without charset, type etc.) and always lowercase. For example if the content type is text/HTML; charset=utf-8 the mimetype would be 'text/html'.

• property mimetype_params: dict[str, str]

  The mimetype parameters as dict. For example if the content type is text/html; charset=utf-8 the params would be {'charset': 'utf-8'}.

• on_json_loading_failed(e)

  Called if get_json() fails and isn’t silenced.

  If this method returns a value, it is used as the return value for get_json(). The default implementation raises BadRequest.

  • Parameters:

    e (ValueError | None) – If parsing failed, this is the exception. It will be None if the content type wasn’t application/json.

    Return type:

    Any

  Changelog

  Changed in version 2.3: Raise a 415 error instead of 400.

• origin

  The host that the request originated from. Set access_control_allow_origin on the response to indicate which origins are allowed.

• parameter_storage_class

  alias of ImmutableMultiDict

• path

  The path part of the URL after root_path. This is the path used for routing within the application.

• property pragma: HeaderSet

  The Pragma general-header field is used to include implementation-specific directives that might apply to any recipient along the request/response chain. All pragma directives specify optional behavior from the viewpoint of the protocol; however, some systems MAY require that behavior be consistent with the directives.

• query_string

  The part of the URL after the “?”. This is the raw value, use args for the parsed values.

• property range: Range | None

  The parsed Range header.

  Changelog

  New in version 0.7.

  • Return type:

    Range

• referrer

  The Referer[sic] request-header field allows the client to specify, for the server’s benefit, the address (URI) of the resource from which the Request-URI was obtained (the “referrer”, although the header field is misspelled).

• remote_addr

  The address of the client sending the request.

• remote_user

  If the server supports user authentication, and the script is protected, this attribute contains the username the user has authenticated as.

• root_path

  The prefix that the application is mounted under, without a trailing slash. path comes after this.

• property root_url: str

  The request URL scheme, host, and root path. This is the root that the application is accessed from.

• routing_exception: HTTPException | None = None

  If matching the URL failed, this is the exception that will be raised / was raised as part of the request handling. This is usually a NotFound exception or something similar.

• scheme

  The URL scheme of the protocol the request used, such as https or wss.

• property script_root: str

  Alias for self.root_path. environ["SCRIPT_ROOT"] without a trailing slash.

• server

  The address of the server. (host, port), (path, None) for unix sockets, or None if not known.

• shallow: bool

  Set when creating the request object. If True, reading from the request body will cause a RuntimeException. Useful to prevent modifying the stream from middleware.

• property stream: IO[bytes]

  The WSGI input stream, with safety checks. This stream can only be consumed once.

  Use get_data() to get the full data as bytes or text. The data attribute will contain the full bytes only if they do not represent form data. The form attribute will contain the parsed form data in that case.

  Unlike input_stream, this stream guards against infinite streams or reading past content_length or max_content_length.

  If max_content_length is set, it can be enforced on streams if wsgi.input_terminated is set. Otherwise, an empty stream is returned.

  If the limit is reached before the underlying stream is exhausted (such as a file that is too large, or an infinite stream), the remaining contents of the stream cannot be read safely. Depending on how the server handles this, clients may show a “connection reset” failure instead of seeing the 413 response.

  Changelog

  Changed in version 2.3: Check max_content_length preemptively and while reading.

  Changed in version 0.9: The stream is always set (but may be consumed) even if form parsing was accessed first.

• trusted_hosts: list[str] | None = None

  Valid host names when handling requests. By default all hosts are trusted, which means that whatever the client says the host is will be accepted.

  Because Host and X-Forwarded-Host headers can be set to any value by a malicious client, it is recommended to either set this property or implement similar validation in the proxy (if the application is being run behind one).

  Changelog

  New in version 0.9.

• property url: str

  The full request URL with the scheme, host, root path, path, and query string.

• property url_root: str

  Alias for root_url. The URL with scheme, host, and root path. For example, https://example.com/app/.

• url_rule: Rule | None = None

  The internal URL rule that matched the request. This can be useful to inspect which methods are allowed for the URL from a before/after handler (request.url_rule.methods) etc. Though if the request’s method was invalid for the URL rule, the valid list is available in routing_exception.valid_methods instead (an attribute of the Werkzeug exception MethodNotAllowed) because the request was never internally bound.

  Changelog

  New in version 0.6.

• property user_agent: UserAgent

  The user agent. Use user_agent.string to get the header value. Set user_agent_class to a subclass of UserAgent to provide parsing for the other properties or other extended data.

  Changelog

  Changed in version 2.1: The built-in parser was removed. Set user_agent_class to a UserAgent subclass to parse data from the string.

• user_agent_class

  alias of UserAgent

• property values: CombinedMultiDict[str, str]

  A werkzeug.datastructures.CombinedMultiDict that combines args and form.

  For GET requests, only args are present, not form.

  Changelog

  Changed in version 2.0: For GET requests, only args are present, not form.

• view_args: dict[str, t.Any] | None = None

  A dict of view arguments that matched the request. If an exception happened when matching, this will be None.

• property want_form_data_parsed: bool

  True if the request method carries content. By default this is true if a Content-Type is sent.

  Changelog

  New in version 0.8.

flask.request

To access incoming request data, you can use the global request object. Flask parses incoming request data for you and gives you access to it through that global object. Internally Flask makes sure that you always get the correct data for the active thread if you are in a multithreaded environment.

This is a proxy. See Notes On Proxies for more information.

The request object is an instance of a Request.

Response Objects

class flask.Response(response=None, status=None, headers=None, mimetype=None, content_type=None, direct_passthrough=False)

The response object that is used by default in Flask. Works like the response object from Werkzeug but is set to have an HTML mimetype by default. Quite often you don’t have to create this object yourself because make_response() will take care of that for you.

If you want to replace the response object used you can subclass this and set response_class to your subclass.

Changelog

Changed in version 1.0: JSON support is added to the response, like the request. This is useful when testing to get the test client response data as JSON.

Changed in version 1.0: Added max_cookie_size.

• Parameters:

  • response (Iterable[str] | Iterable[bytes]) –

  • status (int | str | HTTPStatus | None) –

  • headers (Headers) –

  • mimetype (str | None) –

  • content_type (str | None) –

  • direct_passthrough (bool) –

• accept_ranges

  The Accept-Ranges header. Even though the name would indicate that multiple values are supported, it must be one string token only.

  The values 'bytes' and 'none' are common.

  Changelog

  New in version 0.7.

• property access_control_allow_credentials: bool

  Whether credentials can be shared by the browser to JavaScript code. As part of the preflight request it indicates whether credentials can be used on the cross origin request.

• access_control_allow_headers

  Which headers can be sent with the cross origin request.

• access_control_allow_methods

  Which methods can be used for the cross origin request.

• access_control_allow_origin

  The origin or ‘*’ for any origin that may make cross origin requests.

• access_control_expose_headers

  Which headers can be shared by the browser to JavaScript code.

• access_control_max_age

  The maximum age in seconds the access control settings can be cached for.

• add_etag(overwrite=False, weak=False)

  Add an etag for the current response if there is none yet.

  Changelog

  Changed in version 2.0: SHA-1 is used to generate the value. MD5 may not be available in some environments.

  • Parameters:

    • overwrite (bool) –

    • weak (bool) –

    Return type:

    None

• age

  The Age response-header field conveys the sender’s estimate of the amount of time since the response (or its revalidation) was generated at the origin server.

  Age values are non-negative decimal integers, representing time in seconds.

• property allow: HeaderSet

  The Allow entity-header field lists the set of methods supported by the resource identified by the Request-URI. The purpose of this field is strictly to inform the recipient of valid methods associated with the resource. An Allow header field MUST be present in a 405 (Method Not Allowed) response.

• autocorrect_location_header = False

  If a redirect Location header is a relative URL, make it an absolute URL, including scheme and domain.

  Changelog

  Changed in version 2.1: This is disabled by default, so responses will send relative redirects.

  New in version 0.8.

• automatically_set_content_length = True

  Should this response object automatically set the content-length header if possible? This is true by default.

  Changelog

  New in version 0.8.

• property cache_control: ResponseCacheControl

  The Cache-Control general-header field is used to specify directives that MUST be obeyed by all caching mechanisms along the request/response chain.

• calculate_content_length()

  Returns the content length if available or None otherwise.

  • Return type:

    int | None

• call_on_close(func)

  Adds a function to the internal list of functions that should be called as part of closing down the response. Since 0.7 this function also returns the function that was passed so that this can be used as a decorator.

  Changelog

  New in version 0.6.

  • Parameters:

    func (Callable[[]__, Any]) –

    Return type:

    Callable[[], Any]

• close()

  Close the wrapped response if possible. You can also use the object in a with statement which will automatically close it.

  Changelog

  New in version 0.9: Can now be used in a with statement.

  • Return type:

    None

• content_encoding

  The Content-Encoding entity-header field is used as a modifier to the media-type. When present, its value indicates what additional content codings have been applied to the entity-body, and thus what decoding mechanisms must be applied in order to obtain the media-type referenced by the Content-Type header field.

• property content_language: HeaderSet

  The Content-Language entity-header field describes the natural language(s) of the intended audience for the enclosed entity. Note that this might not be equivalent to all the languages used within the entity-body.

• content_length

  The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.

• content_location

  The Content-Location entity-header field MAY be used to supply the resource location for the entity enclosed in the message when that entity is accessible from a location separate from the requested resource’s URI.

• content_md5

  The Content-MD5 entity-header field, as defined in RFC 1864, is an MD5 digest of the entity-body for the purpose of providing an end-to-end message integrity check (MIC) of the entity-body. (Note: a MIC is good for detecting accidental modification of the entity-body in transit, but is not proof against malicious attacks.)

• property content_range: ContentRange

  The Content-Range header as a ContentRange object. Available even if the header is not set.

  Changelog

  New in version 0.7.

• property content_security_policy: ContentSecurityPolicy

  The Content-Security-Policy header as a ContentSecurityPolicy object. Available even if the header is not set.

  The Content-Security-Policy header adds an additional layer of security to help detect and mitigate certain types of attacks.

• property content_security_policy_report_only: ContentSecurityPolicy

  The Content-Security-policy-report-only header as a ContentSecurityPolicy object. Available even if the header is not set.

  The Content-Security-Policy-Report-Only header adds a csp policy that is not enforced but is reported thereby helping detect certain types of attacks.

• content_type

  The Content-Type entity-header field indicates the media type of the entity-body sent to the recipient or, in the case of the HEAD method, the media type that would have been sent had the request been a GET.

• cross_origin_embedder_policy

  Prevents a document from loading any cross-origin resources that do not explicitly grant the document permission. Values must be a member of the werkzeug.http.COEP enum.

• cross_origin_opener_policy

  Allows control over sharing of browsing context group with cross-origin documents. Values must be a member of the werkzeug.http.COOP enum.

• property data: bytes | str

  A descriptor that calls get_data() and set_data().

• date

  The Date general-header field represents the date and time at which the message was originated, having the same semantics as orig-date in RFC 822.

  Changelog

  Changed in version 2.0: The datetime object is timezone-aware.

• default_mimetype: str | None = ‘text/html’

  the default mimetype if none is provided.

• default_status = 200

  the default status if none is provided.

• delete_cookie(key, path=’/‘, domain=None, secure=False, httponly=False, samesite=None)

  Delete a cookie. Fails silently if key doesn’t exist.

  • Parameters:

    • key (str) – the key (name) of the cookie to be deleted.

    • path (str | None) – if the cookie that should be deleted was limited to a path, the path has to be defined here.

    • domain (str | None) – if the cookie that should be deleted was limited to a domain, that domain has to be defined here.

    • secure (bool) – If True, the cookie will only be available via HTTPS.

    • httponly (bool) – Disallow JavaScript access to the cookie.

    • samesite (str | None) – Limit the scope of the cookie to only be attached to requests that are “same-site”.

    Return type:

    None

• direct_passthrough

  Pass the response body directly through as the WSGI iterable. This can be used when the body is a binary file or other iterator of bytes, to skip some unnecessary checks. Use send_file() instead of setting this manually.

• expires

  The Expires entity-header field gives the date/time after which the response is considered stale. A stale cache entry may not normally be returned by a cache.

  Changelog

  Changed in version 2.0: The datetime object is timezone-aware.

• classmethod force_type(response, environ=None)

  Enforce that the WSGI response is a response object of the current type. Werkzeug will use the Response internally in many situations like the exceptions. If you call get_response() on an exception you will get back a regular Response object, even if you are using a custom subclass.

  This method can enforce a given response type, and it will also convert arbitrary WSGI callables into response objects if an environ is provided:

  # convert a Werkzeug response object into an instance of the
  # MyResponseClass subclass.
  response = MyResponseClass.force_type(response)
  # convert any WSGI application into a response object
  response = MyResponseClass.force_type(response, environ)

  This is especially useful if you want to post-process responses in the main dispatcher and use functionality provided by your subclass.

  Keep in mind that this will modify response objects in place if possible!

  • Parameters:

    • response (Response) – a response object or wsgi application.

    • environ (WSGIEnvironment | None) – a WSGI environment object.

    Returns:

    a response object.

    Return type:

    Response

• freeze()

  Make the response object ready to be pickled. Does the following:

  • Buffer the response into a list, ignoring implicity_sequence_conversion and direct_passthrough.

  • Set the Content-Length header.

  • Generate an ETag header if one is not already set.

  Changelog

  Changed in version 2.1: Removed the no_etag parameter.

  Changed in version 2.0: An ETag header is always added.

  Changed in version 0.6: The Content-Length header is set.

  • Return type:

    None

• classmethod from_app(app, environ, buffered=False)

  Create a new response object from an application output. This works best if you pass it an application that returns a generator all the time. Sometimes applications may use the write() callable returned by the start_response function. This tries to resolve such edge cases automatically. But if you don’t get the expected output you should set buffered to True which enforces buffering.

  • Parameters:

    • app (WSGIApplication) – the WSGI application to execute.

    • environ (WSGIEnvironment) – the WSGI environment to execute against.

    • buffered (bool) – set to True to enforce buffering.

    Returns:

    a response object.

    Return type:

    Response

• get_app_iter(environ)

  Returns the application iterator for the given environ. Depending on the request method and the current status code the return value might be an empty response rather than the one from the response.

  If the request method is HEAD or the status code is in a range where the HTTP specification requires an empty response, an empty iterable is returned.

  Changelog

  New in version 0.6.

  • Parameters:

    environ (WSGIEnvironment) – the WSGI environment of the request.

    Returns:

    a response iterable.

    Return type:

    t.Iterable[bytes]

• get_data(as_text=False)

  The string representation of the response body. Whenever you call this property the response iterable is encoded and flattened. This can lead to unwanted behavior if you stream big data.

  This behavior can be disabled by setting implicit_sequence_conversion to False.

  If as_text is set to True the return value will be a decoded string.

  Changelog

  New in version 0.9.

  • Parameters:

    as_text (bool) –

    Return type:

    bytes | str

• get_etag()

  Return a tuple in the form (etag, is_weak). If there is no ETag the return value is (None, None).

  • Return type:

    tuple[str, bool] | tuple[None, None]

• get_json(force=False, silent=False)

  Parse data as JSON. Useful during testing.

  If the mimetype does not indicate JSON (application/json, see is_json), this returns None.

  Unlike Request.get_json(), the result is not cached.

  • Parameters:

    • force (bool) – Ignore the mimetype and always try to parse JSON.

    • silent (bool) – Silence parsing errors and return None instead.

    Return type:

    Any | None

• get_wsgi_headers(environ)

  This is automatically called right before the response is started and returns headers modified for the given environment. It returns a copy of the headers from the response with some modifications applied if necessary.

  For example the location header (if present) is joined with the root URL of the environment. Also the content length is automatically set to zero here for certain status codes.

  Changelog

  Changed in version 0.6: Previously that function was called fix_headers and modified the response object in place. Also since 0.6, IRIs in location and content-location headers are handled properly.

  Also starting with 0.6, Werkzeug will attempt to set the content length if it is able to figure it out on its own. This is the case if all the strings in the response iterable are already encoded and the iterable is buffered.

  • Parameters:

    environ (WSGIEnvironment) – the WSGI environment of the request.

    Returns:

    returns a new Headers object.

    Return type:

    Headers

• get_wsgi_response(environ)

  Returns the final WSGI response as tuple. The first item in the tuple is the application iterator, the second the status and the third the list of headers. The response returned is created specially for the given environment. For example if the request method in the WSGI environment is 'HEAD' the response will be empty and only the headers and status code will be present.

  Changelog

  New in version 0.6.

  • Parameters:

    environ (WSGIEnvironment) – the WSGI environment of the request.

    Returns:

    an (app_iter, status, headers) tuple.

    Return type:

    tuple[t.Iterable[bytes], str, list[tuple[str, str]]]

• implicit_sequence_conversion = True

  if set to False accessing properties on the response object will not try to consume the response iterator and convert it into a list.

  Changelog

  New in version 0.6.2: That attribute was previously called implicit_seqence_conversion. (Notice the typo). If you did use this feature, you have to adapt your code to the name change.

• property is_json: bool

  Check if the mimetype indicates JSON data, either application/json or application/*+json.

• property is_sequence: bool

  If the iterator is buffered, this property will be True. A response object will consider an iterator to be buffered if the response attribute is a list or tuple.

  Changelog

  New in version 0.6.

• property is_streamed: bool

  If the response is streamed (the response is not an iterable with a length information) this property is True. In this case streamed means that there is no information about the number of iterations. This is usually True if a generator is passed to the response object.

  This is useful for checking before applying some sort of post filtering that should not take place for streamed responses.

• iter_encoded()

  Iter the response encoded with the encoding of the response. If the response object is invoked as WSGI application the return value of this method is used as application iterator unless direct_passthrough was activated.

  • Return type:

    Iterator[bytes]

• property json: Any | None

  The parsed JSON data if mimetype indicates JSON (application/json, see is_json).

  Calls get_json() with default arguments.

• last_modified

  The Last-Modified entity-header field indicates the date and time at which the origin server believes the variant was last modified.

  Changelog

  Changed in version 2.0: The datetime object is timezone-aware.

• location

  The Location response-header field is used to redirect the recipient to a location other than the Request-URI for completion of the request or identification of a new resource.

• make_conditional(request_or_environ, accept_ranges=False, complete_length=None)

  Make the response conditional to the request. This method works best if an etag was defined for the response already. The add_etag method can be used to do that. If called without etag just the date header is set.

  This does nothing if the request method in the request or environ is anything but GET or HEAD.

  For optimal performance when handling range requests, it’s recommended that your response data object implements seekable, seek and tell methods as described by io.IOBase. Objects returned by wrap_file() automatically implement those methods.

  It does not remove the body of the response because that’s something the __call__() function does for us automatically.

  Returns self so that you can do return resp.make_conditional(req) but modifies the object in-place.

  • Parameters:

    • request_or_environ (WSGIEnvironment | Request) – a request object or WSGI environment to be used to make the response conditional against.

    • accept_ranges (bool | str) – This parameter dictates the value of Accept-Ranges header. If False (default), the header is not set. If True, it will be set to "bytes". If it’s a string, it will use this value.

    • complete_length (int | None) – Will be used only in valid Range Requests. It will set Content-Range complete length value and compute Content-Length real value. This parameter is mandatory for successful Range Requests completion.

    Raises:

    RequestedRangeNotSatisfiable if Range header could not be parsed or satisfied.

    Return type:

    Response

  Changelog

  Changed in version 2.0: Range processing is skipped if length is 0 instead of raising a 416 Range Not Satisfiable error.

• make_sequence()

  Converts the response iterator in a list. By default this happens automatically if required. If implicit_sequence_conversion is disabled, this method is not automatically called and some properties might raise exceptions. This also encodes all the items.

  Changelog

  New in version 0.6.

  • Return type:

    None

• property max_cookie_size: int

  Read-only view of the MAX_COOKIE_SIZE config key.

  See max_cookie_size in Werkzeug’s docs.

• property mimetype: str | None

  The mimetype (content type without charset etc.)

• property mimetype_params: dict[str, str]

  The mimetype parameters as dict. For example if the content type is text/html; charset=utf-8 the params would be {'charset': 'utf-8'}.

  Changelog

  New in version 0.5.

• response: t.Iterable[str] | t.Iterable[bytes]

  The response body to send as the WSGI iterable. A list of strings or bytes represents a fixed-length response, any other iterable is a streaming response. Strings are encoded to bytes as UTF-8.

  Do not set to a plain string or bytes, that will cause sending the response to be very inefficient as it will iterate one byte at a time.

• property retry_after: datetime | None

  The Retry-After response-header field can be used with a 503 (Service Unavailable) response to indicate how long the service is expected to be unavailable to the requesting client.

  Time in seconds until expiration or date.

  Changelog

  Changed in version 2.0: The datetime object is timezone-aware.

• set_cookie(key, value=’’, max_age=None, expires=None, path=’/‘, domain=None, secure=False, httponly=False, samesite=None)

  Sets a cookie.

  A warning is raised if the size of the cookie header exceeds max_cookie_size, but the header will still be set.

  • Parameters:

    • key (str) – the key (name) of the cookie to be set.

    • value (str) – the value of the cookie.

    • max_age (timedelta | int | None) – should be a number of seconds, or None (default) if the cookie should last only as long as the client’s browser session.

    • expires (str | datetime | int | float | None) – should be a datetime object or UNIX timestamp.

    • path (str | None) – limits the cookie to a given path, per default it will span the whole domain.

    • domain (str | None) – if you want to set a cross-domain cookie. For example, domain="example.com" will set a cookie that is readable by the domain www.example.com, foo.example.com etc. Otherwise, a cookie will only be readable by the domain that set it.

    • secure (bool) – If True, the cookie will only be available via HTTPS.

    • httponly (bool) – Disallow JavaScript access to the cookie.

    • samesite (str | None) – Limit the scope of the cookie to only be attached to requests that are “same-site”.

    Return type:

    None

• set_data(value)

  Sets a new string as response. The value must be a string or bytes. If a string is set it’s encoded to the charset of the response (utf-8 by default).

  Changelog

  New in version 0.9.

  • Parameters:

    value (bytes | str) –

    Return type:

    None

• set_etag(etag, weak=False)

  Set the etag, and override the old one if there was one.

  • Parameters:

    • etag (str) –

    • weak (bool) –

    Return type:

    None

• property status: str

  The HTTP status code as a string.

• property status_code: int

  The HTTP status code as a number.

• property stream: ResponseStream

  The response iterable as write-only stream.

• property vary: HeaderSet

  The Vary field value indicates the set of request-header fields that fully determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request without revalidation.

• property www_authenticate: WWWAuthenticate

  The WWW-Authenticate header parsed into a WWWAuthenticate object. Modifying the object will modify the header value.

  This header is not set by default. To set this header, assign an instance of WWWAuthenticate to this attribute.

  response.www_authenticate = WWWAuthenticate(
      "basic", {"realm": "Authentication Required"}
  )

  Multiple values for this header can be sent to give the client multiple options. Assign a list to set multiple headers. However, modifying the items in the list will not automatically update the header values, and accessing this attribute will only ever return the first value.

  To unset this header, assign None or use del.

  Changelog

  Changed in version 2.3: This attribute can be assigned to to set the header. A list can be assigned to set multiple header values. Use del to unset the header.

  Changed in version 2.3: WWWAuthenticate is no longer a dict. The token attribute was added for auth challenges that use a token instead of parameters.

Sessions

If you have set Flask.secret_key (or configured it from SECRET_KEY) you can use sessions in Flask applications. A session makes it possible to remember information from one request to another. The way Flask does this is by using a signed cookie. The user can look at the session contents, but can’t modify it unless they know the secret key, so make sure to set that to something complex and unguessable.

To access the current session you can use the session object:

class flask.session

The session object works pretty much like an ordinary dict, with the difference that it keeps track of modifications.

This is a proxy. See Notes On Proxies for more information.

The following attributes are interesting:

• new

  True if the session is new, False otherwise.

• modified

  True if the session object detected a modification. Be advised that modifications on mutable structures are not picked up automatically, in that situation you have to explicitly set the attribute to True yourself. Here an example:

  # this change is not picked up because a mutable object (here
  # a list) is changed.
  session['objects'].append(42)
  # so mark it as modified yourself
  session.modified = True

• permanent

  If set to True the session lives for permanent_session_lifetime seconds. The default is 31 days. If set to False (which is the default) the session will be deleted when the user closes the browser.

Session Interface

Changelog

New in version 0.8.

The session interface provides a simple way to replace the session implementation that Flask is using.

class flask.sessions.SessionInterface

The basic interface you have to implement in order to replace the default session interface which uses werkzeug’s securecookie implementation. The only methods you have to implement are open_session() and save_session(), the others have useful defaults which you don’t need to change.

The session object returned by the open_session() method has to provide a dictionary like interface plus the properties and methods from the SessionMixin. We recommend just subclassing a dict and adding that mixin:

class Session(dict, SessionMixin):
    pass

If open_session() returns None Flask will call into make_null_session() to create a session that acts as replacement if the session support cannot work because some requirement is not fulfilled. The default NullSession class that is created will complain that the secret key was not set.

To replace the session interface on an application all you have to do is to assign flask.Flask.session_interface:

app = Flask(__name__)
app.session_interface = MySessionInterface()

Multiple requests with the same session may be sent and handled concurrently. When implementing a new session interface, consider whether reads or writes to the backing store must be synchronized. There is no guarantee on the order in which the session for each request is opened or saved, it will occur in the order that requests begin and end processing.

Changelog

New in version 0.8.

• get_cookie_domain(app)

  The value of the Domain parameter on the session cookie. If not set, browsers will only send the cookie to the exact domain it was set from. Otherwise, they will send it to any subdomain of the given value as well.

  Uses the SESSION_COOKIE_DOMAIN config.

  Changelog

  Changed in version 2.3: Not set by default, does not fall back to SERVER_NAME.

  • Parameters:

    app (Flask) –

    Return type:

    str | None

• get_cookie_httponly(app)

  Returns True if the session cookie should be httponly. This currently just returns the value of the SESSION_COOKIE_HTTPONLY config var.

  • Parameters:

    app (Flask) –

    Return type:

    bool

• get_cookie_name(app)

  The name of the session cookie. Uses``app.config[“SESSION_COOKIE_NAME”]``.

  • Parameters:

    app (Flask) –

    Return type:

    str

• get_cookie_path(app)

  Returns the path for which the cookie should be valid. The default implementation uses the value from the SESSION_COOKIE_PATH config var if it’s set, and falls back to APPLICATION_ROOT or uses / if it’s None.

  • Parameters:

    app (Flask) –

    Return type:

    str

• get_cookie_samesite(app)

  Return 'Strict' or 'Lax' if the cookie should use the SameSite attribute. This currently just returns the value of the SESSION_COOKIE_SAMESITE setting.

  • Parameters:

    app (Flask) –

    Return type:

    str | None

• get_cookie_secure(app)

  Returns True if the cookie should be secure. This currently just returns the value of the SESSION_COOKIE_SECURE setting.

  • Parameters:

    app (Flask) –

    Return type:

    bool

• get_expiration_time(app, session)

  A helper method that returns an expiration date for the session or None if the session is linked to the browser session. The default implementation returns now + the permanent session lifetime configured on the application.

  • Parameters:

    • app (Flask) –

    • session (SessionMixin) –

    Return type:

    datetime | None

• is_null_session(obj)

  Checks if a given object is a null session. Null sessions are not asked to be saved.

  This checks if the object is an instance of null_session_class by default.

  • Parameters:

    obj (object) –

    Return type:

    bool

• make_null_session(app)

  Creates a null session which acts as a replacement object if the real session support could not be loaded due to a configuration error. This mainly aids the user experience because the job of the null session is to still support lookup without complaining but modifications are answered with a helpful error message of what failed.

  This creates an instance of null_session_class by default.

  • Parameters:

    app (Flask) –

    Return type:

    NullSession

• null_session_class

  make_null_session() will look here for the class that should be created when a null session is requested. Likewise the is_null_session() method will perform a typecheck against this type.

  alias of NullSession

• open_session(app, request)

  This is called at the beginning of each request, after pushing the request context, before matching the URL.

  This must return an object which implements a dictionary-like interface as well as the SessionMixin interface.

  This will return None to indicate that loading failed in some way that is not immediately an error. The request context will fall back to using make_null_session() in this case.

  • Parameters:

    • app (Flask) –

    • request (Request) –

    Return type:

    SessionMixin | None

• pickle_based = False

  A flag that indicates if the session interface is pickle based. This can be used by Flask extensions to make a decision in regards to how to deal with the session object.

  Changelog

  New in version 0.10.

• save_session(app, session, response)

  This is called at the end of each request, after generating a response, before removing the request context. It is skipped if is_null_session() returns True.

  • Parameters:

    • app (Flask) –

    • session (SessionMixin) –

    • response (Response) –

    Return type:

    None

• should_set_cookie(app, session)

  Used by session backends to determine if a Set-Cookie header should be set for this session cookie for this response. If the session has been modified, the cookie is set. If the session is permanent and the SESSION_REFRESH_EACH_REQUEST config is true, the cookie is always set.

  This check is usually skipped if the session was deleted.

  Changelog

  New in version 0.11.

  • Parameters:

    • app (Flask) –

    • session (SessionMixin) –

    Return type:

    bool

class flask.sessions.SecureCookieSessionInterface

The default session interface that stores sessions in signed cookies through the itsdangerous module.

• static digest_method(string=b’’, *, usedforsecurity=True)

  the hash function to use for the signature. The default is sha1

• key_derivation = ‘hmac’

  the name of the itsdangerous supported key derivation. The default is hmac.

• open_session(app, request)

  This is called at the beginning of each request, after pushing the request context, before matching the URL.

  This must return an object which implements a dictionary-like interface as well as the SessionMixin interface.

  This will return None to indicate that loading failed in some way that is not immediately an error. The request context will fall back to using make_null_session() in this case.

  • Parameters:

    • app (Flask) –

    • request (Request) –

    Return type:

    SecureCookieSession | None

• salt = ‘cookie-session’

  the salt that should be applied on top of the secret key for the signing of cookie based sessions.

• save_session(app, session, response)

  This is called at the end of each request, after generating a response, before removing the request context. It is skipped if is_null_session() returns True.

  • Parameters:

    • app (Flask) –

    • session (SessionMixin) –

    • response (Response) –

    Return type:

    None

• serializer = <flask.json.tag.TaggedJSONSerializer object>

  A python serializer for the payload. The default is a compact JSON derived serializer with support for some extra Python types such as datetime objects or tuples.

• session_class

  alias of SecureCookieSession

class flask.sessions.SecureCookieSession(initial=None)

Base class for sessions based on signed cookies.

This session backend will set the modified and accessed attributes. It cannot reliably track whether a session is new (vs. empty), so new remains hard coded to False.

• Parameters:

  initial (t.Any) –

• accessed = False

  header, which allows caching proxies to cache different pages for different users.

• get(key, default=None)

  Return the value for key if key is in the dictionary, else default.

  • Parameters:

    • key (str) –

    • default (Any) –

    Return type:

    Any

• modified = False

  When data is changed, this is set to True. Only the session dictionary itself is tracked; if the session contains mutable data (for example a nested dict) then this must be set to True manually when modifying that data. The session cookie will only be written to the response if this is True.

• setdefault(key, default=None)

  Insert key with a value of default if key is not in the dictionary.

  Return the value for key if key is in the dictionary, else default.

  • Parameters:

    • key (str) –

    • default (Any) –

    Return type:

    Any

class flask.sessions.NullSession(initial=None)

Class used to generate nicer error messages if sessions are not available. Will still allow read-only access to the empty session but fail on setting.

• Parameters:

  initial (t.Any) –

• clear() → None. Remove all items from D.

  • Parameters:

    • args (Any) –

    • kwargs (Any) –

    Return type:

    NoReturn

• pop(k[, d]) → v, remove specified key and return the corresponding value.

  If the key is not found, return the default if given; otherwise, raise a KeyError.

  • Parameters:

    • args (Any) –

    • kwargs (Any) –

    Return type:

    NoReturn

• popitem(*args, **kwargs)

  Remove and return a (key, value) pair as a 2-tuple.

  Pairs are returned in LIFO (last-in, first-out) order. Raises KeyError if the dict is empty.

  • Parameters:

    • args (Any) –

    • kwargs (Any) –

    Return type:

    NoReturn

• setdefault(*args, **kwargs)

  Insert key with a value of default if key is not in the dictionary.

  Return the value for key if key is in the dictionary, else default.

  • Parameters:

    • args (Any) –

    • kwargs (Any) –

    Return type:

    NoReturn

• update([E, ]**F) → None. Update D from dict/iterable E and F.

  If E is present and has a .keys() method, then does: for k in E: D[k] = E[k] If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k]

  • Parameters:

    • args (Any) –

    • kwargs (Any) –

    Return type:

    NoReturn

class flask.sessions.SessionMixin

Expands a basic dictionary with session attributes.

• accessed = True

  Some implementations can detect when session data is read or written and set this when that happens. The mixin default is hard coded to True.

• modified = True

  Some implementations can detect changes to the session and set this when that happens. The mixin default is hard coded to True.

• property permanent: bool

  This reflects the '_permanent' key in the dict.

Notice

The PERMANENT_SESSION_LIFETIME config can be an integer or timedelta. The permanent_session_lifetime attribute is always a timedelta.

Test Client

class flask.testing.FlaskClient(*args, **kwargs)

Works like a regular Werkzeug test client but has knowledge about Flask’s contexts to defer the cleanup of the request context until the end of a with block. For general information about how to use this class refer to werkzeug.test.Client.

Changelog

Changed in version 0.12: app.test_client() includes preset default environment, which can be set after instantiation of the app.test_client() object in client.environ_base.

Basic usage is outlined in the Testing Flask Applications chapter.

• Parameters:

  • args (t.Any) –

  • kwargs (t.Any) –

• open(*args, buffered=False, follow_redirects=False, **kwargs)

  Generate an environ dict from the given arguments, make a request to the application using it, and return the response.

  • Parameters:

    • args (t.Any) – Passed to EnvironBuilder to create the environ for the request. If a single arg is passed, it can be an existing EnvironBuilder or an environ dict.

    • buffered (bool) – Convert the iterator returned by the app into a list. If the iterator has a close() method, it is called automatically.

    • follow_redirects (bool) – Make additional requests to follow HTTP redirects until a non-redirect status is returned. TestResponse.history lists the intermediate responses.

    • kwargs (t.Any) –

    Return type:

    TestResponse

  Changelog

  Changed in version 2.1: Removed the as_tuple parameter.

  Changed in version 2.0: The request input stream is closed when calling response.close(). Input streams for redirects are automatically closed.

  Changed in version 0.5: If a dict is provided as file in the dict for the data parameter the content type has to be called content_type instead of mimetype. This change was made for consistency with werkzeug.FileWrapper.

  Changed in version 0.5: Added the follow_redirects parameter.

• session_transaction(*args, **kwargs)

  When used in combination with a with statement this opens a session transaction. This can be used to modify the session that the test client uses. Once the with block is left the session is stored back.

  with client.session_transaction() as session:
      session['value'] = 42

  Internally this is implemented by going through a temporary test request context and since session handling could depend on request variables this function accepts the same arguments as test_request_context() which are directly passed through.

  • Parameters:

    • args (Any) –

    • kwargs (Any) –

    Return type:

    Iterator[SessionMixin]

Test CLI Runner

class flask.testing.FlaskCliRunner(app, **kwargs)

A CliRunner for testing a Flask app’s CLI commands. Typically created using test_cli_runner(). See Running Commands with the CLI Runner.

• Parameters:

  • app (Flask) –

  • kwargs (t.Any) –

• invoke(cli=None, args=None, **kwargs)

  Invokes a CLI command in an isolated environment. See CliRunner.invoke for full method documentation. See Running Commands with the CLI Runner for examples.

  If the obj argument is not given, passes an instance of ScriptInfo that knows how to load the Flask app being tested.

  • Parameters:

    • cli (Any) – Command object to invoke. Default is the app’s cli group.

    • args (Any) – List of strings to invoke the command with.

    • kwargs (Any) –

    Returns:

    a Result object.

    Return type:

    Any

Application Globals

To share data that is valid for one request only from one function to another, a global variable is not good enough because it would break in threaded environments. Flask provides you with a special object that ensures it is only valid for the active request and that will return different values for each request. In a nutshell: it does the right thing, like it does for request and session.

flask.g

A namespace object that can store data during an application context. This is an instance of Flask.app_ctx_globals_class, which defaults to ctx._AppCtxGlobals.

This is a good place to store resources during a request. For example, a before_request function could load a user object from a session id, then set g.user to be used in the view function.

This is a proxy. See Notes On Proxies for more information.

Changelog

Changed in version 0.10: Bound to the application context instead of the request context.

class flask.ctx._AppCtxGlobals

A plain object. Used as a namespace for storing data during an application context.

Creating an app context automatically creates this object, which is made available as the g proxy.

• ‘key’ in g

  Check whether an attribute is present.

  Changelog

  New in version 0.10.

• iter(g)

  Return an iterator over the attribute names.

  Changelog

  New in version 0.10.

• get(name, default=None)

  Get an attribute by name, or a default value. Like dict.get().

  • Parameters:

    • name (str) – Name of attribute to get.

    • default (Any | None) – Value to return if the attribute is not present.

    Return type:

    Any

  Changelog

  New in version 0.10.

• pop(name, default=<object object>)

  Get and remove an attribute by name. Like dict.pop().

  • Parameters:

    • name (str) – Name of attribute to pop.

    • default (Any) – Value to return if the attribute is not present, instead of raising a KeyError.

    Return type:

    Any

  Changelog

  New in version 0.11.

• setdefault(name, default=None)

  Get the value of an attribute if it is present, otherwise set and return a default value. Like dict.setdefault().

  • Parameters:

    • name (str) – Name of attribute to get.

    • default (Any) – Value to set and return if the attribute is not present.

    Return type:

    Any

  Changelog

  New in version 0.11.

Useful Functions and Classes

flask.current_app

A proxy to the application handling the current request. This is useful to access the application without needing to import it, or if it can’t be imported, such as when using the application factory pattern or in blueprints and extensions.

This is only available when an application context is pushed. This happens automatically during requests and CLI commands. It can be controlled manually with app_context().

This is a proxy. See Notes On Proxies for more information.

flask.has_request_context()

If you have code that wants to test if a request context is there or not this function can be used. For instance, you may want to take advantage of request information if the request object is available, but fail silently if it is unavailable.

class User(db.Model):
    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and has_request_context():
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

Alternatively you can also just test any of the context bound objects (such as request or g) for truthness:

class User(db.Model):
    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and request:
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

Changelog

New in version 0.7.

• Return type:

  bool

flask.copy_current_request_context(f)

A helper function that decorates a function to retain the current request context. This is useful when working with greenlets. The moment the function is decorated a copy of the request context is created and then pushed when the function is called. The current session is also included in the copied request context.

Example:

import gevent
from flask import copy_current_request_context
@app.route('/')
def index():
    @copy_current_request_context
    def do_some_work():
        # do some work here, it can access flask.request or
        # flask.session like you would otherwise in the view function.
        ...
    gevent.spawn(do_some_work)
    return 'Regular response'

Changelog

New in version 0.10.

• Parameters:

  f (F) –

  Return type:

  F

flask.has_app_context()

Works like has_request_context() but for the application context. You can also just do a boolean check on the current_app object instead.

Changelog

New in version 0.9.

• Return type:

  bool

flask.url_for(endpoint, *, _anchor=None, _method=None, _scheme=None, _external=None, **values)

Generate a URL to the given endpoint with the given values.

This requires an active request or application context, and calls current_app.url_for(). See that method for full documentation.

• Parameters:

  • endpoint (str) – The endpoint name associated with the URL to generate. If this starts with a ., the current blueprint name (if any) will be used.

  • _anchor (str | None) – If given, append this as #anchor to the URL.

  • _method (str | None) – If given, generate the URL associated with this method for the endpoint.

  • _scheme (str | None) – If given, the URL will have this scheme if it is external.

  • _external (bool | None) – If given, prefer the URL to be internal (False) or require it to be external (True). External URLs include the scheme and domain. When not in an active request, URLs are external by default.

  • values (Any) – Values to use for the variable parts of the URL rule. Unknown keys are appended as query string arguments, like ?a=b&c=d.

  Return type:

  str

Changelog

Changed in version 2.2: Calls current_app.url_for, allowing an app to override the behavior.

Changed in version 0.10: The _scheme parameter was added.

Changed in version 0.9: The _anchor and _method parameters were added.

Changed in version 0.9: Calls app.handle_url_build_error on build errors.

flask.abort(code, *args, **kwargs)

Raise an HTTPException for the given status code.

If current_app is available, it will call its aborter object, otherwise it will use werkzeug.exceptions.abort().

• Parameters:

  • code (int | Response) – The status code for the exception, which must be registered in app.aborter.

  • args (Any) – Passed to the exception.

  • kwargs (Any) – Passed to the exception.

  Return type:

  NoReturn

Changelog

New in version 2.2: Calls current_app.aborter if available instead of always using Werkzeug’s default abort.

flask.redirect(location, code=302, Response=None)

Create a redirect response object.

If current_app is available, it will use its redirect() method, otherwise it will use werkzeug.utils.redirect().

• Parameters:

  • location (str) – The URL to redirect to.

  • code (int) – The status code for the redirect.

  • Response (type[Response] | None) – The response class to use. Not used when current_app is active, which uses app.response_class.

  Return type:

  Response

Changelog

New in version 2.2: Calls current_app.redirect if available instead of always using Werkzeug’s default redirect.

flask.make_response(*args)

Sometimes it is necessary to set additional headers in a view. Because views do not have to return response objects but can return a value that is converted into a response object by Flask itself, it becomes tricky to add headers to it. This function can be called instead of using a return and you will get a response object which you can use to attach headers.

If view looked like this and you want to add a new header:

def index():
    return render_template('index.html', foo=42)

You can now do something like this:

def index():
    response = make_response(render_template('index.html', foo=42))
    response.headers['X-Parachutes'] = 'parachutes are cool'
    return response

This function accepts the very same arguments you can return from a view function. This for example creates a response with a 404 error code:

response = make_response(render_template('not_found.html'), 404)

The other use case of this function is to force the return value of a view function into a response which is helpful with view decorators:

response = make_response(view_function())
response.headers['X-Parachutes'] = 'parachutes are cool'

Internally this function does the following things:

• if no arguments are passed, it creates a new response argument

• if one argument is passed, flask.Flask.make_response() is invoked with it.

• if more than one argument is passed, the arguments are passed to the flask.Flask.make_response() function as tuple.

Changelog

New in version 0.6.

• Parameters:

  args (t.Any) –

  Return type:

  Response

flask.after_this_request(f)

Executes a function after this request. This is useful to modify response objects. The function is passed the response object and has to return the same or a new one.

Example:

@app.route('/')
def index():
    @after_this_request
    def add_header(response):
        response.headers['X-Foo'] = 'Parachute'
        return response
    return 'Hello World!'

This is more useful if a function other than the view function wants to modify a response. For instance think of a decorator that wants to add some headers without converting the return value into a response object.

Changelog

New in version 0.9.

• Parameters:

  f (Callable[__[Any]__, Any] | Callable[__[Any]__, Awaitable[Any]__]) –

  Return type:

  Callable[[Any], Any] | Callable[[Any], Awaitable[Any]]

flask.send_file(path_or_file, mimetype=None, as_attachment=False, download_name=None, conditional=True, etag=True, last_modified=None, max_age=None)

Send the contents of a file to the client.

The first argument can be a file path or a file-like object. Paths are preferred in most cases because Werkzeug can manage the file and get extra information from the path. Passing a file-like object requires that the file is opened in binary mode, and is mostly useful when building a file in memory with io.BytesIO.

Never pass file paths provided by a user. The path is assumed to be trusted, so a user could craft a path to access a file you didn’t intend. Use send_from_directory() to safely serve user-requested paths from within a directory.

If the WSGI server sets a file_wrapper in environ, it is used, otherwise Werkzeug’s built-in wrapper is used. Alternatively, if the HTTP server supports X-Sendfile, configuring Flask with USE_X_SENDFILE = True will tell the server to send the given path, which is much more efficient than reading it in Python.

• Parameters:

  • path_or_file (os.PathLike[t.AnyStr] | str | t.BinaryIO) – The path to the file to send, relative to the current working directory if a relative path is given. Alternatively, a file-like object opened in binary mode. Make sure the file pointer is seeked to the start of the data.

  • mimetype (str | None) – The MIME type to send for the file. If not provided, it will try to detect it from the file name.

  • as_attachment (bool) – Indicate to a browser that it should offer to save the file instead of displaying it.

  • download_name (str | None) – The default name browsers will use when saving the file. Defaults to the passed file name.

  • conditional (bool) – Enable conditional and range responses based on request headers. Requires passing a file path and environ.

  • etag (bool | str) – Calculate an ETag for the file, which requires passing a file path. Can also be a string to use instead.

  • last_modified (datetime | int | float | None) – The last modified time to send for the file, in seconds. If not provided, it will try to detect it from the file path.

  • max_age (None | (int | t.Callable[[str | None], int | None])) – How long the client should cache the file, in seconds. If set, Cache-Control will be public, otherwise it will be no-cache to prefer conditional caching.

  Return type:

  Response

Changelog

Changed in version 2.0: download_name replaces the attachment_filename parameter. If as_attachment=False, it is passed with Content-Disposition: inline instead.

Changed in version 2.0: max_age replaces the cache_timeout parameter. conditional is enabled and max_age is not set by default.

Changed in version 2.0: etag replaces the add_etags parameter. It can be a string to use instead of generating one.

Changed in version 2.0: Passing a file-like object that inherits from TextIOBase will raise a ValueError rather than sending an empty file.

New in version 2.0: Moved the implementation to Werkzeug. This is now a wrapper to pass some Flask-specific arguments.

Changed in version 1.1: filename may be a PathLike object.

Changed in version 1.1: Passing a BytesIO object supports range requests.

Changed in version 1.0.3: Filenames are encoded with ASCII instead of Latin-1 for broader compatibility with WSGI servers.

Changed in version 1.0: UTF-8 filenames as specified in RFC 2231 are supported.

Changed in version 0.12: The filename is no longer automatically inferred from file objects. If you want to use automatic MIME and etag support, pass a filename via filename_or_fp or attachment_filename.

Changed in version 0.12: attachment_filename is preferred over filename for MIME detection.

Changed in version 0.9: cache_timeout defaults to Flask.get_send_file_max_age().

Changed in version 0.7: MIME guessing and etag support for file-like objects was removed because it was unreliable. Pass a filename if you are able to, otherwise attach an etag yourself.

Changed in version 0.5: The add_etags, cache_timeout and conditional parameters were added. The default behavior is to add etags.

New in version 0.2.

flask.send_from_directory(directory, path, **kwargs)

Send a file from within a directory using send_file().

@app.route("/uploads/<path:name>")
def download_file(name):
    return send_from_directory(
        app.config['UPLOAD_FOLDER'], name, as_attachment=True
    )

This is a secure way to serve files from a folder, such as static files or uploads. Uses safe_join() to ensure the path coming from the client is not maliciously crafted to point outside the specified directory.

If the final path does not point to an existing regular file, raises a 404 NotFound error.

• Parameters:

  • directory (os.PathLike[str] | str) – The directory that path must be located under, relative to the current application’s root path.

  • path (os.PathLike[str] | str) – The path to the file to send, relative to directory.

  • kwargs (t.Any) – Arguments to pass to send_file().

  Return type:

  Response

Changelog

Changed in version 2.0: path replaces the filename parameter.

New in version 2.0: Moved the implementation to Werkzeug. This is now a wrapper to pass some Flask-specific arguments.

New in version 0.5.

Message Flashing

flask.flash(message, category=’message’)

Flashes a message to the next request. In order to remove the flashed message from the session and to display it to the user, the template has to call get_flashed_messages().

Changelog

Changed in version 0.3: category parameter added.

• Parameters:

  • message (str) – the message to be flashed.

  • category (str) – the category for the message. The following values are recommended: 'message' for any kind of message, 'error' for errors, 'info' for information messages and 'warning' for warnings. However any kind of string can be used as category.

  Return type:

  None

flask.get_flashed_messages(with_categories=False, category_filter=())

Pulls all flashed messages from the session and returns them. Further calls in the same request to the function will return the same messages. By default just the messages are returned, but when with_categories is set to True, the return value will be a list of tuples in the form (category, message) instead.

Filter the flashed messages to one or more categories by providing those categories in category_filter. This allows rendering categories in separate html blocks. The with_categories and category_filter arguments are distinct:

• with_categories controls whether categories are returned with message text (True gives a tuple, where False gives just the message text).

• category_filter filters the messages down to only those matching the provided categories.

See Message Flashing for examples.

Changelog

Changed in version 0.9: category_filter parameter added.

Changed in version 0.3: with_categories parameter added.

• Parameters:

  • with_categories (bool) – set to True to also receive categories.

  • category_filter (Iterable[str]) – filter of categories to limit return values. Only categories in the list will be returned.

  Return type:

  list[str] | list[tuple[str, str]]

JSON Support

Flask uses Python’s built-in json module for handling JSON by default. The JSON implementation can be changed by assigning a different provider to flask.Flask.json_provider_class or flask.Flask.json. The functions provided by flask.json will use methods on app.json if an app context is active.

Jinja’s |tojson filter is configured to use the app’s JSON provider. The filter marks the output with |safe. Use it to render data inside HTML <script> tags.

<script>
    const names = {{ names|tojson }};
    renderChart(names, {{ axis_data|tojson }});
</script>

flask.json.jsonify(*args, **kwargs)

Serialize the given arguments as JSON, and return a Response object with the application/json mimetype. A dict or list returned from a view will be converted to a JSON response automatically without needing to call this.

This requires an active request or application context, and calls app.json.response().

In debug mode, the output is formatted with indentation to make it easier to read. This may also be controlled by the provider.

Either positional or keyword arguments can be given, not both. If no arguments are given, None is serialized.

• Parameters:

  • args (t.Any) – A single value to serialize, or multiple values to treat as a list to serialize.

  • kwargs (t.Any) – Treat as a dict to serialize.

  Return type:

  Response

Changelog

Changed in version 2.2: Calls current_app.json.response, allowing an app to override the behavior.

Changed in version 2.0.2: decimal.Decimal is supported by converting to a string.

Changed in version 0.11: Added support for serializing top-level arrays. This was a security risk in ancient browsers. See JSON Security.

New in version 0.2.

flask.json.dumps(obj, **kwargs)

Serialize data as JSON.

If current_app is available, it will use its app.json.dumps() method, otherwise it will use json.dumps().

• Parameters:

  • obj (Any) – The data to serialize.

  • kwargs (Any) – Arguments passed to the dumps implementation.

  Return type:

  str

Changelog

Changed in version 2.3: The app parameter was removed.

Changed in version 2.2: Calls current_app.json.dumps, allowing an app to override the behavior.

Changed in version 2.0.2: decimal.Decimal is supported by converting to a string.

Changed in version 2.0: encoding will be removed in Flask 2.1.

Changed in version 1.0.3: app can be passed directly, rather than requiring an app context for configuration.

flask.json.dump(obj, fp, **kwargs)

Serialize data as JSON and write to a file.

If current_app is available, it will use its app.json.dump() method, otherwise it will use json.dump().

• Parameters:

  • obj (Any) – The data to serialize.

  • fp (IO[str]) – A file opened for writing text. Should use the UTF-8 encoding to be valid JSON.

  • kwargs (Any) – Arguments passed to the dump implementation.

  Return type:

  None

Changelog

Changed in version 2.3: The app parameter was removed.

Changed in version 2.2: Calls current_app.json.dump, allowing an app to override the behavior.

Changed in version 2.0: Writing to a binary file, and the encoding argument, will be removed in Flask 2.1.

flask.json.loads(s, **kwargs)

Deserialize data as JSON.

If current_app is available, it will use its app.json.loads() method, otherwise it will use json.loads().

• Parameters:

  • s (str | bytes) – Text or UTF-8 bytes.

  • kwargs (Any) – Arguments passed to the loads implementation.

  Return type:

  Any

Changelog

Changed in version 2.3: The app parameter was removed.

Changed in version 2.2: Calls current_app.json.loads, allowing an app to override the behavior.

Changed in version 2.0: encoding will be removed in Flask 2.1. The data must be a string or UTF-8 bytes.

Changed in version 1.0.3: app can be passed directly, rather than requiring an app context for configuration.

flask.json.load(fp, **kwargs)

Deserialize data as JSON read from a file.

If current_app is available, it will use its app.json.load() method, otherwise it will use json.load().

• Parameters:

  • fp (IO) – A file opened for reading text or UTF-8 bytes.

  • kwargs (Any) – Arguments passed to the load implementation.

  Return type:

  Any

Changelog

Changed in version 2.3: The app parameter was removed.

Changed in version 2.2: Calls current_app.json.load, allowing an app to override the behavior.

Changed in version 2.2: The app parameter will be removed in Flask 2.3.

Changed in version 2.0: encoding will be removed in Flask 2.1. The file must be text mode, or binary mode with UTF-8 bytes.

class flask.json.provider.JSONProvider(app)