venv —- 创建虚拟环境

3.3 新版功能.

源码：Lib/venv/

venv 模块支持使用自己的站点目录创建轻量级“虚拟环境”，可选择与系统站点目录隔离。每个虚拟环境都有自己的 Python 二进制文件（与用于创建此环境的二进制文件的版本相匹配），并且可以在其站点目录中拥有自己独立的已安装 Python 软件包集。

有关 Python 虚拟环境的更多信息，请参阅 PEP 405 。

参见

Python 软件包用户指南：创建和使用虚拟环境

注解

从 Python 3.6 开始，不推荐使用 pyvenv 脚本，而是使用 python3 -m venv 来帮助防止任何关于虚拟环境将基于哪个 Python 解释器的混淆。

创建虚拟环境

通过执行 venv 指令来创建一个 虚拟环境:

  1. python3 -m venv /path/to/new/virtual/environment

Running this command creates the target directory (creating any parentdirectories that don't exist already) and places a pyvenv.cfg file in itwith a home key pointing to the Python installation from which the commandwas run. It also creates a bin (or Scripts on Windows) subdirectorycontaining a copy/symlink of the Python binary/binaries (as appropriate for theplatform or arguments used at environment creation time). It also creates an(initially empty) lib/pythonX.Y/site-packages subdirectory(on Windows, this is Lib\site-packages). If an existingdirectory is specified, it will be re-used.

3.6 版后已移除: pyvenv 是 Python 3.3 和 3.4 中创建虚拟环境的推荐工具，不过 在 Python 3.6 中已弃用。

在 3.5 版更改: 现在推荐使用 venv 来创建虚拟环境。

On Windows, invoke the venv command as follows:

  1. c:\>c:\Python35\python -m venv c:\path\to\myenv

Alternatively, if you configured the PATH and PATHEXT variables foryour Python installation:

  1. c:\>python -m venv c:\path\to\myenv

The command, if run with -h, will show the available options:

  1. usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
  2.             [--upgrade] [--without-pip] [--prompt PROMPT]
  3.             ENV_DIR [ENV_DIR ...]
  4.  
  5. Creates virtual Python environments in one or more target directories.
  6.  
  7. positional arguments:
  8.   ENV_DIR               A directory to create the environment in.
  9.  
  10. optional arguments:
  11.   -h, --help            show this help message and exit
  12.   --system-site-packages
  13.                         Give the virtual environment access to the system
  14.                         site-packages dir.
  15.   --symlinks            Try to use symlinks rather than copies, when symlinks
  16.                         are not the default for the platform.
  17.   --copies              Try to use copies rather than symlinks, even when
  18.                         symlinks are the default for the platform.
  19.   --clear               Delete the contents of the environment directory if it
  20.                         already exists, before environment creation.
  21.   --upgrade             Upgrade the environment directory to use this version
  22.                         of Python, assuming Python has been upgraded in-place.
  23.   --without-pip         Skips installing or upgrading pip in the virtual
  24.                         environment (pip is bootstrapped by default)
  25.   --prompt PROMPT       Provides an alternative prompt prefix for this
  26.                         environment.
  27.  
  28. Once an environment has been created, you may wish to activate it, e.g. by
  29. sourcing an activate script in its bin directory.

在 3.4 版更改: Installs pip by default, added the —without-pip and —copiesoptions

在 3.4 版更改: In earlier versions, if the target directory already existed, an error wasraised, unless the —clear or —upgrade option was provided.

注解

While symlinks are supported on Windows, they are not recommended. Ofparticular note is that double-clicking python.exe in File Explorerwill resolve the symlink eagerly and ignore the virtual environment.

The created pyvenv.cfg file also includes theinclude-system-site-packages key, set to true if venv isrun with the —system-site-packages option, false otherwise.

Unless the —without-pip option is given, ensurepip will beinvoked to bootstrap pip into the virtual environment.

Multiple paths can be given to venv, in which case an identical virtualenvironment will be created, according to the given options, at each providedpath.

Once a virtual environment has been created, it can be "activated" using ascript in the virtual environment's binary directory. The invocation of thescript is platform-specific (<venv> must be replaced by the path of thedirectory containing the virtual environment):

平台Shell用于激活虚拟环境的命令
Posixbash/zsh$ source <venv>/bin/activate
fish$ . <venv>/bin/activate.fish
csh/tcsh$ source <venv>/bin/activate.csh
Windowscmd.exeC:\> <venv>\Scripts\activate.bat
PowerShellPS C:\> <venv>\Scripts\Activate.ps1

You don't specifically need to activate an environment; activation justprepends the virtual environment's binary directory to your path, so that"python" invokes the virtual environment's Python interpreter and you can runinstalled scripts without having to use their full path. However, all scriptsinstalled in a virtual environment should be runnable without activating it,and run with the virtual environment's Python automatically.

You can deactivate a virtual environment by typing "deactivate" in your shell.The exact mechanism is platform-specific and is an internal implementationdetail (typically a script or shell function will be used).

3.4 新版功能: fish and csh activation scripts.

注解

A virtual environment is a Python environment such that the Pythoninterpreter, libraries and scripts installed into it are isolated from thoseinstalled in other virtual environments, and (by default) any librariesinstalled in a "system" Python, i.e., one which is installed as part of youroperating system.

A virtual environment is a directory tree which contains Python executablefiles and other files which indicate that it is a virtual environment.

Common installation tools such as setuptools and pip work asexpected with virtual environments. In other words, when a virtualenvironment is active, they install Python packages into the virtualenvironment without needing to be told to do so explicitly.

When a virtual environment is active (i.e., the virtual environment's Pythoninterpreter is running), the attributes sys.prefix andsys.exec_prefix point to the base directory of the virtualenvironment, whereas sys.base_prefix andsys.base_exec_prefix point to the non-virtual environment Pythoninstallation which was used to create the virtual environment. If a virtualenvironment is not active, then sys.prefix is the same assys.base_prefix and sys.exec_prefix is the same assys.base_exec_prefix (they all point to a non-virtual environmentPython installation).

When a virtual environment is active, any options that change theinstallation path will be ignored from all distutils configurationfiles to prevent projects being inadvertently installed outside of thevirtual environment.

When working in a command shell, users can make a virtual environment activeby running an activate script in the virtual environment's executablesdirectory (the precise filename and command to use the file isshell-dependent), which prepends the virtual environment's directory forexecutables to the PATH environment variable for the running shell. Thereshould be no need in other circumstances to activate a virtualenvironment; scripts installed into virtual environments have a "shebang"line which points to the virtual environment's Python interpreter. This meansthat the script will run with that interpreter regardless of the value ofPATH. On Windows, "shebang" line processing is supported if you have thePython Launcher for Windows installed (this was added to Python in 3.3 - seePEP 397 for more details). Thus, double-clicking an installed script in aWindows Explorer window should run the script with the correct interpreterwithout there needing to be any reference to its virtual environment inPATH.

API

The high-level method described above makes use of a simple API which providesmechanisms for third-party virtual environment creators to customize environmentcreation according to their needs, the EnvBuilder class.

  • class venv.EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False, with_pip=False, prompt=None)

  • The EnvBuilder class accepts the following keyword arguments oninstantiation:

    • system_site_packages — a Boolean value indicating that the system Pythonsite-packages should be available to the environment (defaults to False).

    • clear — a Boolean value which, if true, will delete the contents ofany existing target directory, before creating the environment.

    • symlinks — a Boolean value indicating whether to attempt to symlink thePython binary rather than copying.

    • upgrade — a Boolean value which, if true, will upgrade an existingenvironment with the running Python - for use when that Python has beenupgraded in-place (defaults to False).

    • with_pip — a Boolean value which, if true, ensures pip isinstalled in the virtual environment. This uses ensurepip withthe —default-pip option.

    • prompt — a String to be used after virtual environment is activated(defaults to None which means directory name of the environment wouldbe used).

在 3.4 版更改: Added the with_pip parameter

3.6 新版功能: Added the prompt parameter

Creators of third-party virtual environment tools will be free to use theprovided EnvBuilder class as a base class.

The returned env-builder is an object which has a method, create:

  • create(env_dir)
  • Create a virtual environment by specifying the target directory(absolute or relative to the current directory) which is to contain thevirtual environment. The create method will either create theenvironment in the specified directory, or raise an appropriateexception.

The create method of the EnvBuilder class illustrates thehooks available for subclass customization:

  1. def create(self, env_dir):
  2.     """
  3.     Create a virtualized Python environment in a directory.
  4.     env_dir is the target directory to create an environment in.
  5.     """
  6.     env_dir = os.path.abspath(env_dir)
  7.     context = self.ensure_directories(env_dir)
  8.     self.create_configuration(context)
  9.     self.setup_python(context)
  10.     self.setup_scripts(context)
  11.     self.post_setup(context)

Each of the methods ensure_directories(),create_configuration(), setup_python(),setup_scripts() and post_setup() can be overridden.

  • ensuredirectories(_env_dir)

  • Creates the environment directory and all necessary directories, andreturns a context object. This is just a holder for attributes (such aspaths), for use by the other methods. The directories are allowed toexist already, as long as either clear or upgrade werespecified to allow operating on an existing environment directory.

  • createconfiguration(_context)

  • Creates the pyvenv.cfg configuration file in the environment.

  • setuppython(_context)

  • Creates a copy or symlink to the Python executable in the environment.On POSIX systems, if a specific executable python3.x was used,symlinks to python and python3 will be created pointing to thatexecutable, unless files with those names already exist.

  • setupscripts(_context)

  • Installs activation scripts appropriate to the platform into the virtualenvironment.

  • postsetup(_context)

  • A placeholder method which can be overridden in third partyimplementations to pre-install packages in the virtual environment orperform other post-creation steps.

在 3.7.2 版更改: Windows now uses redirector scripts for python[w].exe instead ofcopying the actual binaries. In 3.7.2 only setup_python() doesnothing unless running from a build in the source tree.

在 3.7.3 版更改: Windows copies the redirector scripts as part of setup_python()instead of setup_scripts(). This was not the case in 3.7.2.When using symlinks, the original executables will be linked.

In addition, EnvBuilder provides this utility method that can becalled from setup_scripts() or post_setup() in subclasses toassist in installing custom scripts into the virtual environment.

  • installscripts(_context, path)

  • path is the path to a directory that should contain subdirectories"common", "posix", "nt", each containing scripts destined for the bindirectory in the environment. The contents of "common" and thedirectory corresponding to os.name are copied after some textreplacement of placeholders:

    • VENV_DIR is replaced with the absolute path of the environmentdirectory.

    • VENV_NAME is replaced with the environment name (final pathsegment of environment directory).

    • VENV_PROMPT is replaced with the prompt (the environmentname surrounded by parentheses and with a following space)

    • VENV_BIN_NAME is replaced with the name of the bin directory(either bin or Scripts).

    • VENV_PYTHON is replaced with the absolute path of theenvironment's executable.

The directories are allowed to exist (for when an existing environmentis being upgraded).

有一个方便实用的模块级别的函数:

  • venv.create(env_dir, system_site_packages=False, clear=False, symlinks=False, with_pip=False, prompt=None)
  • 通过关键词参数来创建一个 EnvBuilder，并且使用 env_dir 参数来调用它的 create() 方法。

3.3 新版功能.

在 3.4 版更改: Added the with_pip parameter

在 3.6 版更改: Added the prompt parameter

一个扩展 EnvBuilder 的例子

下面的脚本展示了如何通过实现一个子类来扩展 EnvBuilder。这个子类会安装 setuptotols 和 pip 的到被创建的虚拟环境中。

  1. import os
  2. import os.path
  3. from subprocess import Popen, PIPE
  4. import sys
  5. from threading import Thread
  6. from urllib.parse import urlparse
  7. from urllib.request import urlretrieve
  8. import venv
  9.  
  10. class ExtendedEnvBuilder(venv.EnvBuilder):
  11.     """
  12.     This builder installs setuptools and pip so that you can pip or
  13.     easy_install other packages into the created virtual environment.
  14.  
  15.     :param nodist: If true, setuptools and pip are not installed into the
  16.                    created virtual environment.
  17.     :param nopip: If true, pip is not installed into the created
  18.                   virtual environment.
  19.     :param progress: If setuptools or pip are installed, the progress of the
  20.                      installation can be monitored by passing a progress
  21.                      callable. If specified, it is called with two
  22.                      arguments: a string indicating some progress, and a
  23.                      context indicating where the string is coming from.
  24.                      The context argument can have one of three values:
  25.                      'main', indicating that it is called from virtualize()
  26.                      itself, and 'stdout' and 'stderr', which are obtained
  27.                      by reading lines from the output streams of a subprocess
  28.                      which is used to install the app.
  29.  
  30.                      If a callable is not specified, default progress
  31.                      information is output to sys.stderr.
  32.     """
  33.  
  34.     def __init__(self, *args, **kwargs):
  35.         self.nodist = kwargs.pop('nodist', False)
  36.         self.nopip = kwargs.pop('nopip', False)
  37.         self.progress = kwargs.pop('progress', None)
  38.         self.verbose = kwargs.pop('verbose', False)
  39.         super().__init__(*args, **kwargs)
  40.  
  41.     def post_setup(self, context):
  42.         """
  43.         Set up any packages which need to be pre-installed into the
  44.         virtual environment being created.
  45.  
  46.         :param context: The information for the virtual environment
  47.                         creation request being processed.
  48.         """
  49.         os.environ['VIRTUAL_ENV'] = context.env_dir
  50.         if not self.nodist:
  51.             self.install_setuptools(context)
  52.         # Can't install pip without setuptools
  53.         if not self.nopip and not self.nodist:
  54.             self.install_pip(context)
  55.  
  56.     def reader(self, stream, context):
  57.         """
  58.         Read lines from a subprocess' output stream and either pass to a progress
  59.         callable (if specified) or write progress information to sys.stderr.
  60.         """
  61.         progress = self.progress
  62.         while True:
  63.             s = stream.readline()
  64.             if not s:
  65.                 break
  66.             if progress is not None:
  67.                 progress(s, context)
  68.             else:
  69.                 if not self.verbose:
  70.                     sys.stderr.write('.')
  71.                 else:
  72.                     sys.stderr.write(s.decode('utf-8'))
  73.                 sys.stderr.flush()
  74.         stream.close()
  75.  
  76.     def install_script(self, context, name, url):
  77.         _, _, path, _, _, _ = urlparse(url)
  78.         fn = os.path.split(path)[-1]
  79.         binpath = context.bin_path
  80.         distpath = os.path.join(binpath, fn)
  81.         # Download script into the virtual environment's binaries folder
  82.         urlretrieve(url, distpath)
  83.         progress = self.progress
  84.         if self.verbose:
  85.             term = '\n'
  86.         else:
  87.             term = ''
  88.         if progress is not None:
  89.             progress('Installing %s ...%s' % (name, term), 'main')
  90.         else:
  91.             sys.stderr.write('Installing %s ...%s' % (name, term))
  92.             sys.stderr.flush()
  93.         # Install in the virtual environment
  94.         args = [context.env_exe, fn]
  95.         p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
  96.         t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
  97.         t1.start()
  98.         t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
  99.         t2.start()
  100.         p.wait()
  101.         t1.join()
  102.         t2.join()
  103.         if progress is not None:
  104.             progress('done.', 'main')
  105.         else:
  106.             sys.stderr.write('done.\n')
  107.         # Clean up - no longer needed
  108.         os.unlink(distpath)
  109.  
  110.     def install_setuptools(self, context):
  111.         """
  112.         Install setuptools in the virtual environment.
  113.  
  114.         :param context: The information for the virtual environment
  115.                         creation request being processed.
  116.         """
  117.         url = 'https://bitbucket.org/pypa/setuptools/downloads/ez_setup.py'
  118.         self.install_script(context, 'setuptools', url)
  119.         # clear up the setuptools archive which gets downloaded
  120.         pred = lambda o: o.startswith('setuptools-') and o.endswith('.tar.gz')
  121.         files = filter(pred, os.listdir(context.bin_path))
  122.         for f in files:
  123.             f = os.path.join(context.bin_path, f)
  124.             os.unlink(f)
  125.  
  126.     def install_pip(self, context):
  127.         """
  128.         Install pip in the virtual environment.
  129.  
  130.         :param context: The information for the virtual environment
  131.                         creation request being processed.
  132.         """
  133.         url = 'https://raw.github.com/pypa/pip/master/contrib/get-pip.py'
  134.         self.install_script(context, 'pip', url)
  135.  
  136. def main(args=None):
  137.     compatible = True
  138.     if sys.version_info < (3, 3):
  139.         compatible = False
  140.     elif not hasattr(sys, 'base_prefix'):
  141.         compatible = False
  142.     if not compatible:
  143.         raise ValueError('This script is only for use with '
  144.                          'Python 3.3 or later')
  145.     else:
  146.         import argparse
  147.  
  148.         parser = argparse.ArgumentParser(prog=__name__,
  149.                                          description='Creates virtual Python '
  150.                                                      'environments in one or '
  151.                                                      'more target '
  152.                                                      'directories.')
  153.         parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
  154.                             help='A directory in which to create the
  155.                                  'virtual environment.')
  156.         parser.add_argument('--no-setuptools', default=False,
  157.                             action='store_true', dest='nodist',
  158.                             help="Don't install setuptools or pip in the "
  159.                                  "virtual environment.")
  160.         parser.add_argument('--no-pip', default=False,
  161.                             action='store_true', dest='nopip',
  162.                             help="Don't install pip in the virtual "
  163.                                  "environment.")
  164.         parser.add_argument('--system-site-packages', default=False,
  165.                             action='store_true', dest='system_site',
  166.                             help='Give the virtual environment access to the '
  167.                                  'system site-packages dir.')
  168.         if os.name == 'nt':
  169.             use_symlinks = False
  170.         else:
  171.             use_symlinks = True
  172.         parser.add_argument('--symlinks', default=use_symlinks,
  173.                             action='store_true', dest='symlinks',
  174.                             help='Try to use symlinks rather than copies, '
  175.                                  'when symlinks are not the default for '
  176.                                  'the platform.')
  177.         parser.add_argument('--clear', default=False, action='store_true',
  178.                             dest='clear', help='Delete the contents of the '
  179.                                                'virtual environment '
  180.                                                'directory if it already '
  181.                                                'exists, before virtual '
  182.                                                'environment creation.')
  183.         parser.add_argument('--upgrade', default=False, action='store_true',
  184.                             dest='upgrade', help='Upgrade the virtual '
  185.                                                  'environment directory to '
  186.                                                  'use this version of '
  187.                                                  'Python, assuming Python '
  188.                                                  'has been upgraded '
  189.                                                  'in-place.')
  190.         parser.add_argument('--verbose', default=False, action='store_true',
  191.                             dest='verbose', help='Display the output '
  192.                                                'from the scripts which '
  193.                                                'install setuptools and pip.')
  194.         options = parser.parse_args(args)
  195.         if options.upgrade and options.clear:
  196.             raise ValueError('you cannot supply --upgrade and --clear together.')
  197.         builder = ExtendedEnvBuilder(system_site_packages=options.system_site,
  198.                                        clear=options.clear,
  199.                                        symlinks=options.symlinks,
  200.                                        upgrade=options.upgrade,
  201.                                        nodist=options.nodist,
  202.                                        nopip=options.nopip,
  203.                                        verbose=options.verbose)
  204.         for d in options.dirs:
  205.             builder.create(d)
  206.  
  207. if __name__ == '__main__':
  208.     rc = 1
  209.     try:
  210.         main()
  211.         rc = 0
  212.     except Exception as e:
  213.         print('Error: %s' % e, file=sys.stderr)
  214.     sys.exit(rc)

这个脚本同样可以 在线下载。