venv --- 创建虚拟环境¶
3.3 新版功能.
源码： 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.
See PEP 405 for more background on Python virtual environments.
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。
3.6 版后已移除: 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 版更改: 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 PATH 和 PATHEXT 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 版更改: 添加 --upgrade-deps 选项，用于将 pip + setuptools 升级到 PyPI 上的最新版本
在 3.4 版更改: 默认安装 pip，并添加 --without-pip 和 --copies 选项
在 3.4 版更改: 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 或 --upgrade 选项。
备注
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。
备注
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 ensurepip 将 pip 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 |
|
fish |
|
|
csh/tcsh |
|
|
PowerShell |
|
|
Windows |
cmd.exe |
|
PowerShell |
|
3.4 新版功能: !fish and !csh activation scripts.
3.8 新版功能: 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 版更改: 添加
with_pip参数3.6 新版功能: 添加
prompt参数3.9 新版功能: 添加
upgrade_deps参数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()和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
EnvBuilderis created with the argclear=True, contents of the environment directory will be cleared and then all necessary subdirectories will be recreated.The returned context object is a
types.SimpleNamespacewith the following attributes:env_dir- The location of the virtual environment. Used for__VENV_DIR__in activation scripts (seeinstall_scripts()).env_name- The name of the virtual environment. Used for__VENV_NAME__in activation scripts (seeinstall_scripts()).prompt- The prompt to be used by the activation scripts. Used for__VENV_PROMPT__in activation scripts (seeinstall_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 (seeinstall_scripts()).env_exe- The name of the Python interpreter in the virtual environment. Used for__VENV_PYTHON__in activation scripts (seeinstall_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 版更改: The attribute
lib_pathwas added to the context, and the context object was documented.在 3.11 版更改: 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python和python3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
pip和setuptools）。通过在环境中使用pip可执行文件来完成。3.9 新版功能.
- 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 版更改: 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 版更改: 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()或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（bin或Scripts）。__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。3.3 新版功能.
在 3.4 版更改: 添加
with_pip参数在 3.6 版更改: 添加
prompt参数在 3.9 版更改: 添加
upgrade_deps参数
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。