venv --- 创建虚拟环境

在 3.3 版本新加入.

原始碼:Lib/venv/


The venv module supports creating lightweight "virtual environments", each with their own independent set of Python packages installed in their site directories. A virtual environment is created on top of an existing Python installation, known as the virtual environment's "base" Python, and may optionally be isolated from the packages in the base environment, so only those explicitly installed in the virtual environment are available.

When used from within a virtual environment, common installation tools such as pip will install Python packages into a virtual environment without needing to be told to do so explicitly.

更多關於 Python 虛擬環境的背景資訊請見 PEP 405

Availability: not Emscripten, not WASI.

This module does not work or is not available on WebAssembly platforms wasm32-emscripten and wasm32-wasi. See WebAssembly platforms for more information.

创建虚拟环境

通过执行 venv 指令来创建一个 虚拟环境:

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

运行此命令将创建目标目录(父目录若不存在也将创建),并放置一个 pyvenv.cfg 文件在其中,文件中有一个 home 键,它的值指向运行此命令的 Python 安装(目标目录的常用名称是 .venv)。它还会创建一个 bin 子目录(在 Windows 上是 Scripts),其中包含 Python 二进制文件的副本或符号链接(视创建环境时使用的平台或参数而定)。它还会创建一个(初始为空的) lib/pythonX.Y/site-packages 子目录(在 Windows 上是 Lib\site-packages)。如果指定了一个现有的目录,这个目录就将被重新使用。

在 3.6 版本開始棄用: pyvenv was the recommended tool for creating virtual environments for Python 3.3 and 3.4, and is deprecated in Python 3.6.

在 3.5 版本變更: 现在推荐使用 venv 来创建虚拟环境。

在 Windows 上,调用 venv 命令如下:

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

或者,如果已经为 Python 安装 配置好 PATHPATHEXT 变量:

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

本命令如果以 -h 参数运行,将显示可用的选项:

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.

在 3.9 版本變更: 添加 --upgrade-deps 选项,用于将 pip + setuptools 升级到 PyPI 上的最新版本

在 3.4 版本變更: 默认安装 pip,并添加 --without-pip--copies 选项

在 3.4 版本變更: 在早期版本中,如果目标目录已存在,将引发错误,除非使用了 --clear--upgrade 选项。

備註

虽然 Windows 支持符号链接,但不推荐使用它们。特别注意,在文件资源管理器中双击 python.exe 将立即解析符号链接,并忽略虚拟环境。

備註

在 Microsoft Windows 上,为了启用 Activate.ps1 脚本,可能需要修改用户的执行策略。可以运行以下 PowerShell 命令来执行此操作:

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

参阅 About Execution Policies 以获取更多信息。

生成的 pyvenv.cfg 文件还包括 include-system-site-packages 键,如果运行 venv 时带有 --system-site-packages 选项,则键值为 true,否则为 false

除非采用 --without-pip 选项,否则将会调用 ensurepippip 引导到虚拟环境中。

可以向 venv 传入多个路径,此时将根据给定的选项,在所给的每个路径上创建相同的虚拟环境。

How venvs work

When a Python interpreter is running from a virtual environment, sys.prefix and sys.exec_prefix point to the directories of the virtual environment, whereas sys.base_prefix and sys.base_exec_prefix point to those of the base Python used to create the environment. It is sufficient to check sys.prefix == sys.base_prefix to determine if the current interpreter is running from a virtual environment.

A virtual environment may be "activated" using a script in its binary directory (bin on POSIX; Scripts on Windows). This will prepend that directory to your PATH, so that running !python will invoke the environment's Python interpreter and you can run installed scripts without having to use their full path. The invocation of the activation script is platform-specific (<venv> must be replaced by the path to the directory containing the virtual environment):

平台

Shell

用于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

$ <venv>/bin/Activate.ps1

Windows

cmd.exe

C:\> <venv>\Scripts\activate.bat

PowerShell

PS C:\> <venv>\Scripts\Activate.ps1

在 3.4 版本新加入: !fish and !csh activation scripts.

在 3.8 版本新加入: 在 POSIX 上安装 PowerShell 激活脚本,以支持 PowerShell Core。

You don't specifically need to activate a virtual environment, as you can just specify the full path to that environment's Python interpreter when invoking Python. Furthermore, all scripts installed in the environment should be runnable without activating it.

In order to achieve this, scripts installed into virtual environments have a "shebang" line which points to the environment's Python interpreter, i.e. #!/<path-to-venv>/bin/python. 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 适用于Windows的Python启动器 installed. Thus, double-clicking an installed script in a Windows Explorer window should run it with the correct interpreter without the environment needing to be activated or on the PATH.

When a virtual environment has been activated, the VIRTUAL_ENV environment variable is set to the path of the environment. Since explicitly activating a virtual environment is not required to use it, VIRTUAL_ENV cannot be relied upon to determine whether a virtual environment is being used.

警告

Because scripts installed in environments should not expect the environment to be activated, their shebang lines contain the absolute paths to their environment's interpreters. Because of this, environments are inherently non-portable, in the general case. You should always have a simple means of recreating an environment (for example, if you have a requirements file requirements.txt, you can invoke pip install -r requirements.txt using the environment's pip to install all of the packages needed by the environment). If for any reason you need to move the environment to a new location, you should recreate it at the desired location and delete the one at the old location. If you move an environment because you moved a parent directory of it, you should recreate the environment in its new location. Otherwise, software installed into the environment may not work as expected.

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).

API

上述的高级方法使用了一个简单的 API,该 API 提供了一种机制,第三方虚拟环境创建者可以根据其需求自定义环境创建过程,该 API 为 EnvBuilder 类。

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

EnvBuilder 类在实例化时接受以下关键字参数:

  • system_site_packages -- 一个布尔值,要求系统 Python 的 site-packages 对环境可用(默认为 False)。

  • clear -- 一个布尔值,如果为 true,则在创建环境前将删除目标目录的现有内容。

  • symlinks -- 一个布尔值,指示是否尝试符号链接 Python 二进制文件,而不是进行复制。

  • upgrade -- 一个布尔值,如果为 true,则将使用当前运行的 Python 去升级一个现有的环境,这主要在原位置的 Python 更新后使用(默认为 False)。

  • with_pip -- 一个布尔值,如果为 true,则确保在虚拟环境中已安装 pip。这使用的是带有 --default-pip 选项的 ensurepip

  • prompt -- 激活虚拟环境后显示的提示符(默认为 None,表示使用环境所在的目录名称)。如果使用了 "." 这一特殊字符串,则使用当前目录的基本名称作为提示符。

  • upgrade_deps -- 将基本 venv 模块更新为 PyPI 上的最新版本。

在 3.4 版本變更: 新增 with_pip 參數

在 3.6 版本新加入: 新增 prompt 參數

在 3.9 版本新加入: 新增 upgrade_deps 參數

第三方虚拟环境工具的创建者可以自由地将此处提供的 EnvBuilder 类作为基类。

返回的 env-builder 是一个对象,包含一个 create 方法:

create(env_dir)

指定要建立虚拟环境的目标目录(绝对路径或相对于当前路径)来创建虚拟环境。create 方法将在指定目录中创建环境,或者引发对应的异常。

EnvBuilder 类的 create 方法定义了可用于定制子类的钩子:

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)

每个方法 ensure_directories(), create_configuration(), setup_python(), setup_scripts()post_setup() 都可以被重写。

ensure_directories(env_dir)

Creates the environment directory and all necessary subdirectories that don't already exist, and returns a context object. This context object is just a holder for attributes (such as paths) for use by the other methods. If the EnvBuilder is created with the arg clear=True, contents of the environment directory will be cleared and then all necessary subdirectories will be recreated.

The returned context object is a types.SimpleNamespace with the following attributes:

  • env_dir - The location of the virtual environment. Used for __VENV_DIR__ in activation scripts (see install_scripts()).

  • env_name - The name of the virtual environment. Used for __VENV_NAME__ in activation scripts (see install_scripts()).

  • prompt - The prompt to be used by the activation scripts. Used for __VENV_PROMPT__ in activation scripts (see install_scripts()).

  • executable - The underlying Python executable used by the virtual environment. This takes into account the case where a virtual environment is created from another virtual environment.

  • inc_path - The include path for the virtual environment.

  • lib_path - The purelib path for the virtual environment.

  • bin_path - The script path for the virtual environment.

  • bin_name - The name of the script path relative to the virtual environment location. Used for __VENV_BIN_NAME__ in activation scripts (see install_scripts()).

  • env_exe - The name of the Python interpreter in the virtual environment. Used for __VENV_PYTHON__ in activation scripts (see install_scripts()).

  • env_exec_cmd - The name of the Python interpreter, taking into account filesystem redirections. This can be used to run Python in the virtual environment.

在 3.12 版本變更: The attribute lib_path was added to the context, and the context object was documented.

在 3.11 版本變更: The venv sysconfig installation scheme is used to construct the paths of the created directories.

create_configuration(context)

在环境中创建 pyvenv.cfg 配置文件。

setup_python(context)

在环境中创建 Python 可执行文件的拷贝或符号链接。在 POSIX 系统上,如果给定了可执行文件 python3.x,将创建指向该可执行文件的 pythonpython3 符号链接,除非相同名称的文件已经存在。

setup_scripts(context)

将适用于平台的激活脚本安装到虚拟环境中。

upgrade_dependencies(context)

升级环境中 venv 依赖的核心软件包(当前为 pipsetuptools)。通过在环境中使用 pip 可执行文件来完成。

在 3.9 版本新加入.

post_setup(context)

占位方法,可以在第三方实现中重写,用于在虚拟环境中预安装软件包,或是其他创建后要执行的步骤。

在 3.7.2 版本變更: Windows 现在为 python[w].exe 使用重定向脚本,而不是复制实际的二进制文件。仅在 3.7.2 中,除非运行的是源码树中的构建,否则 setup_python() 不会执行任何操作。

在 3.7.3 版本變更: Windows 将重定向脚本复制为 setup_python() 的一部分而非 setup_scripts()。在 3.7.2 中不是这种情况。使用符号链接时,将链接至原始可执行文件。

此外,EnvBuilder 提供了如下实用方法,可以从子类的 setup_scripts()post_setup() 调用,用来将自定义脚本安装到虚拟环境中。

install_scripts(context, path)

path 是一个目录的路径,该目录应包含子目录 "common", "posix", "nt",每个子目录存有发往对应环境中 bin 目录的脚本。在下列占位符替换完毕后,将复制 "common" 的内容和与 os.name 对应的子目录:

  • __VENV_DIR__ 会被替换为环境目录的绝对路径。

  • __VENV_NAME__ 会被替换为环境名称(环境目录的最后一个字段)。

  • __VENV_PROMPT__ 会被替换为提示符(用括号括起来的环境名称紧跟着一个空格)。

  • __VENV_BIN_NAME__ 会被替换为 bin 目录的名称( binScripts )。

  • __VENV_PYTHON__ 会被替换为环境可执行文件的绝对路径。

允许目录已存在(用于升级现有环境时)。

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, upgrade_deps=False)

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。

在 3.3 版本新加入.

在 3.4 版本變更: 新增 with_pip 參數

在 3.6 版本變更: 新增 prompt 參數

在 3.9 版本變更: 新增 upgrade_deps 參數

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 setuptools 和 pip 到被创建的虚拟环境中。

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)

这个脚本同样可以 在线下载