venv — Creation of virtual environments创建虚拟环境

New in version 3.3.版本3.3中新增。

Source code: Lib/venv/

---

The venv module provides support for creating lightweight “virtual environments” with their own site directories, optionally isolated from system site directories. venv模块支持创建具有自己的站点目录的轻量级“虚拟环境”，可以选择与系统站点目录隔离。Each virtual environment has its own Python binary (which matches the version of the binary that was used to create this environment) and can have its own independent set of installed Python packages in its site directories.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版本相匹配），并且可以在其站点目录中有自己独立的一组已安装的Python包。

See PEP 405 for more information about Python virtual environments.有关Python虚拟环境的更多信息，请参阅PEP 405。

See also

Python Packaging User Guide: Creating and using virtual environmentsPython打包用户指南：创建和使用虚拟环境

Creating virtual environments创建虚拟环境

Creation of virtual environments is done by executing the command venv:虚拟环境的创建是通过执行命令venv来完成的：

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

Running this command creates the target directory (creating any parent directories that don’t exist already) and places a pyvenv.cfg file in it with a home key pointing to the Python installation from which the command was run (a common name for the target directory is .venv). 运行此命令会创建目标目录（创建任何不存在的父目录），并在其中放置一个pyvenv.cfg文件，该文件带有指向运行该命令的Python安装的home键（目标目录的通用名称为.venv）。It also creates a bin (or Scripts on Windows) subdirectory containing a copy/symlink of the Python binary/binaries (as appropriate for the platform or arguments used at environment creation time). 它还创建了一个bin（或Windows上的Scripts）子目录，其中包含Python二进制文件/二进制文件的副本/symlink（适用于环境创建时使用的平台或参数）。It also creates an (initially empty) lib/pythonX.Y/site-packages subdirectory (on Windows, this is Lib\site-packages). 它还创建了一个（最初为空）lib/pythonX.Y/site-packages子目录（在Windows上，这是Lib\site-packages）。If an existing directory is specified, it will be re-used.如果指定了现有目录，则会重新使用该目录。

Deprecated since version 3.6: 自3.6版以来已弃用：pyvenv was the recommended tool for creating virtual environments for Python 3.3 and 3.4, and is deprecated in Python 3.6.pyvenv是为Python 3.3和3.4创建虚拟环境的推荐工具，在Python 3.6中已被弃用。

Changed in version 3.5:版本3.5中更改： The use of venv is now recommended for creating virtual environments.现在建议使用venv来创建虚拟环境。

On Windows, invoke the venv command as follows:在Windows上，按如下方式调用venv命令：

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

Alternatively, if you configured the PATH and PATHEXT variables for your Python installation:或者，如果您为Python安装配置了PATH和PATHEXT变量：

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

The command, if run with -h, will show the available options:如果使用-h运行该命令，将显示可用选项：

usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
            [--upgrade] [--without-pip] [--prompt PROMPT] [--upgrade-deps]
            ENV_DIR [ENV_DIR ...]
Creates virtual Python environments in one or more target directories.

positional arguments:
  ENV_DIR               A directory to create the environment in.

optional arguments:
  -h, --help            show this help message and exit
  --system-site-packages
                        Give the virtual environment access to the system
                        site-packages dir.
  --symlinks            Try to use symlinks rather than copies, when symlinks
                        are not the default for the platform.
  --copies              Try to use copies rather than symlinks, even when
                        symlinks are the default for the platform.
  --clear               Delete the contents of the environment directory if it
                        already exists, before environment creation.
  --upgrade             Upgrade the environment directory to use this version
                        of Python, assuming Python has been upgraded in-place.
  --without-pip         Skips installing or upgrading pip in the virtual
                        environment (pip is bootstrapped by default)
  --prompt PROMPT       Provides an alternative prompt prefix for this
                        environment.
  --upgrade-deps        Upgrade core dependencies: pip setuptools to the
                        latest version in PyPI

Once an environment has been created, you may wish to activate it, e.g. by
sourcing an activate script in its bin directory.

Changed in version 3.9:版本3.9中更改： Add --upgrade-deps option to upgrade pip + setuptools to the latest on PyPI添加--upgrade-deps选项，将pip+setuptools升级到PyPI上的最新版本

Changed in version 3.4:版本3.4中更改： Installs pip by default, added the --without-pip and --copies options默认情况下安装pip，添加了--without-pip和--copies选项

Changed in version 3.4:版本3.4中更改： In earlier versions, if the target directory already existed, an error was raised, unless the --clear or --upgrade option was provided.在早期版本中，如果目标目录已经存在，则会引发错误，除非提供了--clear或--upgrade选项。

Note

While symlinks are supported on Windows, they are not recommended. 虽然Windows支持符号链接，但不建议使用符号链接。Of particular note is that double-clicking python.exe in File Explorer will resolve the symlink eagerly and ignore the virtual environment.特别值得注意的是，在文件资源管理器中双击python.exe将急切地解析符号链接，并忽略虚拟环境。

Note

On Microsoft Windows, it may be required to enable the Activate.ps1 script by setting the execution policy for the user. 在Microsoft Windows上，可能需要通过设置用户的执行策略来启用Activate.ps1脚本。You can do this by issuing the following PowerShell command:您可以通过发出以下PowerShell命令来执行此操作：

PS C:> Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser

See About Execution Policies for more information.有关详细信息，请参阅关于执行策略。

The created pyvenv.cfg file also includes the include-system-site-packages key, set to true if venv is run with the --system-site-packages option, false otherwise.创建的pyvenv.cfg文件还包括include-system-site-packages键，如果使用--system-site-packages选项运行venv，则该键设置为true，否则设置为false。

Unless the --without-pip option is given, ensurepip will be invoked to bootstrap pip into the virtual environment.除非给出--without-pip选项，否则将调用ensurepip将pip引导到虚拟环境中。

Multiple paths can be given to venv, in which case an identical virtual environment will be created, according to the given options, at each provided path.可以为venv提供多个路径，在这种情况下，将根据给定的选项，在每个提供的路径上创建相同的虚拟环境。

Once a virtual environment has been created, it can be “activated” using a script in the virtual environment’s binary directory. 一旦创建了虚拟环境，就可以使用虚拟环境二进制目录中的脚本来“激活”它。The invocation of the script is platform-specific (<venv> must be replaced by the path of the directory containing the virtual environment):脚本的调用是特定于平台的（<venv>必须替换为包含虚拟环境的目录的路径）：

Platform站台	Shell	Command to activate virtual environment激活虚拟环境的命令
POSIX	bash/zsh	$ source <venv>/bin/activate
	fish	$ source <venv>/bin/activate.fish
	csh/tcsh	$ source <venv>/bin/activate.csh
	PowerShell Core	$ <venv>/bin/Activate.ps1
Windows	cmd.exe	C:\> <venv>\Scripts\activate.bat
	PowerShell	PS C:\> <venv>\Scripts\Activate.ps1

When a virtual environment is active, the VIRTUAL_ENV environment variable is set to the path of the virtual environment. This can be used to check if one is running inside a virtual environment.

You don’t specifically need to activate an environment; activation just prepends the virtual environment’s binary directory to your path, so that “python” invokes the virtual environment’s Python interpreter and you can run installed scripts without having to use their full path. However, all scripts installed 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 implementation detail (typically a script or shell function will be used).

New in version 3.4.版本3.4中新增。fish and csh activation scripts.

New in version 3.8.版本3.8中新增。PowerShell activation scripts installed under POSIX for PowerShell Core support.

Note

A virtual environment is a Python environment such that the Python interpreter, libraries and scripts installed into it are isolated from those installed in other virtual environments, and (by default) any libraries installed in a “system” Python, i.e., one which is installed as part of your operating system.

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

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

When a virtual environment is active (i.e., the virtual environment’s Python interpreter is running), the attributes sys.prefix and sys.exec_prefix point to the base directory of the virtual environment, whereas sys.base_prefix and sys.base_exec_prefix point to the non-virtual environment Python installation which was used to create the virtual environment. If a virtual environment is not active, then sys.prefix is the same as sys.base_prefix and sys.exec_prefix is the same as sys.base_exec_prefix (they all point to a non-virtual environment Python installation).

When a virtual environment is active, any options that change the installation path will be ignored from all distutils configuration files to prevent projects being inadvertently installed outside of the virtual environment.

When working in a command shell, users can make a virtual environment active by running an activate script in the virtual environment’s executables directory (the precise filename and command to use the file is shell-dependent), which prepends the virtual environment’s directory for executables to the PATH environment variable for the running shell. There should be no need in other circumstances to activate a virtual environment; scripts installed into virtual environments have a “shebang” line which points to the virtual environment’s Python interpreter. This means that the script will run with that interpreter regardless of the value of PATH. On Windows, “shebang” line processing is supported if you have the Python Launcher for Windows installed (this was added to Python in 3.3 - see PEP 397 for more details). Thus, double-clicking an installed script in a Windows Explorer window should run the script with the correct interpreter without there needing to be any reference to its virtual environment in PATH.

API

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

classvenv.EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False, with_pip=False, prompt=None, upgrade_deps=False)

The EnvBuilder class accepts the following keyword arguments on instantiation:

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

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

• symlinks – a Boolean value indicating whether to attempt to symlink the Python binary rather than copying.

• upgrade – a Boolean value which, if true, will upgrade an existing environment with the running Python - for use when that Python has been upgraded in-place (defaults to False).

• with_pip – a Boolean value which, if true, ensures pip is installed in the virtual environment. This uses ensurepip with the --default-pip option.

• prompt – a String to be used after virtual environment is activated (defaults to None which means directory name of the environment would be used). If the special string "." is provided, the basename of the current directory is used as the prompt.

• upgrade_deps – Update the base venv modules to the latest on PyPI

Changed in version 3.4:版本3.4中更改： Added the with_pip parameter

New in version 3.6.版本3.6中新增。Added the prompt parameter

New in version 3.9.版本3.9中新增。Added the upgrade_deps parameter

Creators of third-party virtual environment tools will be free to use the provided 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 the virtual environment. The create method will either create the environment in the specified directory, or raise an appropriate exception.

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

def create(self, env_dir):
    """
    Create a virtualized Python environment in a directory.
    env_dir is the target directory to create an environment in.
    """
    env_dir = os.path.abspath(env_dir)
    context = self.ensure_directories(env_dir)
    self.create_configuration(context)
    self.setup_python(context)
    self.setup_scripts(context)
    self.post_setup(context)

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

ensure_directories(env_dir)

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

create_configuration(context)

Creates the pyvenv.cfg configuration file in the environment.

setup_python(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 that executable, unless files with those names already exist.

setup_scripts(context)

Installs activation scripts appropriate to the platform into the virtual environment.

upgrade_dependencies(context)

Upgrades the core venv dependency packages (currently pip and setuptools) in the environment. This is done by shelling out to the pip executable in the environment.

New in version 3.9.版本3.9中新增。

post_setup(context)

A placeholder method which can be overridden in third party implementations to pre-install packages in the virtual environment or perform other post-creation steps.

Changed in version 3.7.2:版本3.7.2中更改： Windows now uses redirector scripts for python[w].exe instead of copying the actual binaries. In 3.7.2 only setup_python() does nothing unless running from a build in the source tree.

Changed in version 3.7.3:版本3.7.3中更改： 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 be called from setup_scripts() or post_setup() in subclasses to assist in installing custom scripts into the virtual environment.

install_scripts(context, path)

path is the path to a directory that should contain subdirectories “common”, “posix”, “nt”, each containing scripts destined for the bin directory in the environment. The contents of “common” and the directory corresponding to os.name are copied after some text replacement of placeholders:

• __VENV_DIR__ is replaced with the absolute path of the environment directory.

• __VENV_NAME__ is replaced with the environment name (final path segment of environment directory).

• __VENV_PROMPT__ is replaced with the prompt (the environment name 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 the environment’s executable.

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

There is also a module-level convenience function:

venv.create(env_dir, system_site_packages=False, clear=False, symlinks=False, with_pip=False, prompt=None, upgrade_deps=False)

Create an EnvBuilder with the given keyword arguments, and call its create() method with the env_dir argument.

New in version 3.3.版本3.3中新增。

Changed in version 3.4:版本3.4中更改： Added the with_pip parameter

Changed in version 3.6:版本3.6中更改： Added the prompt parameter

Changed in version 3.9:版本3.9中更改： Added the upgrade_deps parameter

An example of extending EnvBuilder

The following script shows how to extend EnvBuilder by implementing a subclass which installs setuptools and pip into a created virtual environment:

import os
import os.path
from subprocess import Popen, PIPE
import sys
from threading import Thread
from urllib.parse import urlparse
from urllib.request import urlretrieve
import venv
class ExtendedEnvBuilder(venv.EnvBuilder):
    """
    This builder installs setuptools and pip so that you can pip or
    easy_install other packages into the created virtual environment.

    :param nodist: If true, setuptools and pip are not installed into the
                   created virtual environment.
    :param nopip: If true, pip is not installed into the created
                  virtual environment.
    :param progress: If setuptools or pip are installed, the progress of the
                     installation can be monitored by passing a progress
                     callable. If specified, it is called with two
                     arguments: a string indicating some progress, and a
                     context indicating where the string is coming from.
                     The context argument can have one of three values:
                     'main', indicating that it is called from virtualize()
                     itself, and 'stdout' and 'stderr', which are obtained
                     by reading lines from the output streams of a subprocess
                     which is used to install the app.

                     If a callable is not specified, default progress
                     information is output to sys.stderr.
    """

    def __init__(self, *args, **kwargs):
        self.nodist = kwargs.pop('nodist', False)
        self.nopip = kwargs.pop('nopip', False)
        self.progress = kwargs.pop('progress', None)
        self.verbose = kwargs.pop('verbose', False)
        super().__init__(*args, **kwargs)

    def post_setup(self, context):
        """
        Set up any packages which need to be pre-installed into the
        virtual environment being created.

        :param context: The information for the virtual environment
                        creation request being processed.
        """
        os.environ['VIRTUAL_ENV'] = context.env_dir
        if not self.nodist:
            self.install_setuptools(context)
        # Can't install pip without setuptools
        if not self.nopip and not self.nodist:
            self.install_pip(context)

    def reader(self, stream, context):
        """
        Read lines from a subprocess' output stream and either pass to a progress
        callable (if specified) or write progress information to sys.stderr.
        """
        progress = self.progress
        while True:
            s = stream.readline()
            if not s:
                break
            if progress is not None:
                progress(s, context)
            else:
                if not self.verbose:
                    sys.stderr.write('.')
                else:
                    sys.stderr.write(s.decode('utf-8'))
                sys.stderr.flush()
        stream.close()

    def install_script(self, context, name, url):
        _, _, path, _, _, _ = urlparse(url)
        fn = os.path.split(path)[-1]
        binpath = context.bin_path
        distpath = os.path.join(binpath, fn)
        # Download script into the virtual environment's binaries folder
        urlretrieve(url, distpath)
        progress = self.progress
        if self.verbose:
            term = '\n'
        else:
            term = ''
        if progress is not None:
            progress('Installing %s ...%s' % (name, term), 'main')
        else:
            sys.stderr.write('Installing %s ...%s' % (name, term))
            sys.stderr.flush()
        # Install in the virtual environment
        args = [context.env_exe, fn]
        p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
        t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
        t1.start()
        t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
        t2.start()
        p.wait()
        t1.join()
        t2.join()
        if progress is not None:
            progress('done.', 'main')
        else:
            sys.stderr.write('done.\n')
        # Clean up - no longer needed
        os.unlink(distpath)

    def install_setuptools(self, context):
        """
        Install setuptools in the virtual environment.

        :param context: The information for the virtual environment
                        creation request being processed.
        """
        url = 'https://bitbucket.org/pypa/setuptools/downloads/ez_setup.py'
        self.install_script(context, 'setuptools', url)
        # clear up the setuptools archive which gets downloaded
        pred = lambda o: o.startswith('setuptools-') and o.endswith('.tar.gz')
        files = filter(pred, os.listdir(context.bin_path))
        for f in files:
            f = os.path.join(context.bin_path, f)
            os.unlink(f)

    def install_pip(self, context):
        """
        Install pip in the virtual environment.

        :param context: The information for the virtual environment
                        creation request being processed.
        """
        url = 'https://bootstrap.pypa.io/get-pip.py'
        self.install_script(context, 'pip', url)

def main(args=None):
    compatible = True
    if sys.version_info < (3, 3):
        compatible = False
    elif not hasattr(sys, 'base_prefix'):
        compatible = False
    if not compatible:
        raise ValueError('This script is only for use with '
                         'Python 3.3 or later')
    else:
        import argparse

        parser = argparse.ArgumentParser(prog=__name__,
                                         description='Creates virtual Python '
                                                     'environments in one or '
                                                     'more target '
                                                     'directories.')
        parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
                            help='A directory in which to create the '
                                 'virtual environment.')
        parser.add_argument('--no-setuptools', default=False,
                            action='store_true', dest='nodist',
                            help="Don't install setuptools or pip in the "
                                 "virtual environment.")
        parser.add_argument('--no-pip', default=False,
                            action='store_true', dest='nopip',
                            help="Don't install pip in the virtual "
                                 "environment.")
        parser.add_argument('--system-site-packages', default=False,
                            action='store_true', dest='system_site',
                            help='Give the virtual environment access to the '
                                 'system site-packages dir.')
        if os.name == 'nt':
            use_symlinks = False
        else:
            use_symlinks = True
        parser.add_argument('--symlinks', default=use_symlinks,
                            action='store_true', dest='symlinks',
                            help='Try to use symlinks rather than copies, '
                                 'when symlinks are not the default for '
                                 'the platform.')
        parser.add_argument('--clear', default=False, action='store_true',
                            dest='clear', help='Delete the contents of the '
                                               'virtual environment '
                                               'directory if it already '
                                               'exists, before virtual '
                                               'environment creation.')
        parser.add_argument('--upgrade', default=False, action='store_true',
                            dest='upgrade', help='Upgrade the virtual '
                                                 'environment directory to '
                                                 'use this version of '
                                                 'Python, assuming Python '
                                                 'has been upgraded '
                                                 'in-place.')
        parser.add_argument('--verbose', default=False, action='store_true',
                            dest='verbose', help='Display the output '
                                               'from the scripts which '
                                               'install setuptools and pip.')
        options = parser.parse_args(args)
        if options.upgrade and options.clear:
            raise ValueError('you cannot supply --upgrade and --clear together.')
        builder = ExtendedEnvBuilder(system_site_packages=options.system_site,
                                       clear=options.clear,
                                       symlinks=options.symlinks,
                                       upgrade=options.upgrade,
                                       nodist=options.nodist,
                                       nopip=options.nopip,
                                       verbose=options.verbose)
        for d in options.dirs:
            builder.create(d)

if __name__ == '__main__':
    rc = 1
    try:
        main()
        rc = 0
    except Exception as e:
        print('Error: %s' % e, file=sys.stderr)
    sys.exit(rc)

This script is also available for download online.