Installation

Python Version

We recommend using the latest version of Python 3. Flask supports Python 3.5and newer, Python 2.7, and PyPy.

Dependencies

These distributions will be installed automatically when installing Flask.

• Werkzeug implements WSGI, the standard Python interface betweenapplications and servers.

• Jinja is a template language that renders the pages your applicationserves.

• MarkupSafe comes with Jinja. It escapes untrusted input when renderingtemplates to avoid injection attacks.

• ItsDangerous securely signs data to ensure its integrity. This is usedto protect Flask’s session cookie.

• Click is a framework for writing command line applications. It providesthe flask command and allows adding custom management commands.

Optional dependencies

These distributions will not be installed automatically. Flask will detect anduse them if you install them.

• Blinker provides support for Signals.

• SimpleJSON is a fast JSON implementation that is compatible withPython’s json module. It is preferred for JSON operations if it isinstalled.

• python-dotenv enables support for Environment Variables From dotenv when running flaskcommands.

• Watchdog provides a faster, more efficient reloader for the developmentserver.

Virtual environments

Use a virtual environment to manage the dependencies for your project, both indevelopment and in production.

What problem does a virtual environment solve? The more Python projects youhave, the more likely it is that you need to work with different versions ofPython libraries, or even Python itself. Newer versions of libraries for oneproject can break compatibility in another project.

Virtual environments are independent groups of Python libraries, one for eachproject. Packages installed for one project will not affect other projects orthe operating system’s packages.

Python 3 comes bundled with the venv module to create virtualenvironments. If you’re using a modern version of Python, you can continue onto the next section.

If you’re using Python 2, see Install virtualenv first.

Create an environment

Create a project folder and a venv folder within:

$ mkdir myproject
$ cd myproject
$ python3 -m venv venv

On Windows:

$ py -3 -m venv venv

If you needed to install virtualenv because you are using Python 2, usethe following command instead:

$ python2 -m virtualenv venv

On Windows:

> \Python27\Scripts\virtualenv.exe venv

Activate the environment

Before you work on your project, activate the corresponding environment:

$ . venv/bin/activate

On Windows:

> venv\Scripts\activate

Your shell prompt will change to show the name of the activated environment.

Install Flask

Within the activated environment, use the following command to install Flask:

$ pip install Flask

Flask is now installed. Check out the Quickstart or go to theDocumentation Overview.

Living on the edge

If you want to work with the latest Flask code before it’s released, install orupdate the code from the master branch:

$ pip install -U https://github.com/pallets/flask/archive/master.tar.gz

Install virtualenv

If you are using Python 2, the venv module is not available. Instead,install virtualenv.

On Linux, virtualenv is provided by your package manager:

# Debian, Ubuntu
$ sudo apt-get install python-virtualenv
 
# CentOS, Fedora
$ sudo yum install python-virtualenv
 
# Arch
$ sudo pacman -S python-virtualenv

If you are on Mac OS X or Windows, download get-pip.py, then:

$ sudo python2 Downloads/get-pip.py
$ sudo python2 -m pip install virtualenv

On Windows, as an administrator:

> \Python27\python.exe Downloads\get-pip.py
> \Python27\python.exe -m pip install virtualenv

Now you can return above and Create an environment.