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venv —- 創(chuàng)建虛擬環(huán)境
3.3 新版功能.

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源碼: 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.
See PEP 405 for more background on Python virtual environments.
參見
Python 打包用戶指南:創(chuàng)建和使用虛擬環(huán)境
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.
創(chuàng)建虛擬環(huán)境
通過執(zhí)行 venv 指令來創(chuàng)建一個 虛擬環(huán)境:
Python3 -m venv /path/to/new/virtual/environment
運行此命令將創(chuàng)建目標目錄(父目錄若不存在也將創(chuàng)建),并放置一個 pyvenv.cfg 文件在其中,文件中有一個 home 鍵,它的值指向運行此命令的 Python 安裝(目標目錄的常用名稱是 .venv)。它還會創(chuàng)建一個 bin 子目錄(在 Windows 上是 Scripts),其中包含 Python 二進制文件的副本或符號鏈接(視創(chuàng)建環(huán)境時使用的平臺或參數(shù)而定)。它還會創(chuàng)建一個(初始為空的) lib/pythonX.Y/site-packages 子目錄(在 Windows 上是 Lib\site-packages)。如果指定了一個現(xiàn)有的目錄,這個目錄就將被重新使用。
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: 現(xiàn)在推薦使用 venv 來創(chuàng)建虛擬環(huán)境。
在 Windows 上,調(diào)用 venv 命令如下:
c:\>c:\Python35\python -m venv c:\path\to\myenv
或者,如果已經(jīng)為 Python 安裝 配置好 PATH 和 PATHEXT 變量:
c:\>python -m venv c:\path\to\myenv
本命令如果以 -h 參數(shù)運行,將顯示可用的選項:
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-packagesGive the virtual environment access to the systemsite-packages dir.--symlinks Try to use symlinks rather than copies, when symlinksare not the default for the platform.--copies Try to use copies rather than symlinks, even whensymlinks are the default for the platform.--clear Delete the contents of the environment directory if italready exists, before environment creation.--upgrade Upgrade the environment directory to use this versionof Python, assuming Python has been upgraded in-place.--without-pip Skips installing or upgrading pip in the virtualenvironment (pip is bootstrapped by default)--prompt PROMPT Provides an alternative prompt prefix for thisenvironment.--upgrade-deps Upgrade core dependencies: pip setuptools to thelatest version in PyPIOnce an environment has been created, you may wish to activate it, e.g. bysourcing an activate script in its bin directory.
在 3.9 版更改: 添加 --upgrade-deps 選項,用于將 pip + setuptools 升級到 PyPI 上的最新版本
在 3.4 版更改: 默認安裝 pip,并添加 --without-pip 和 --copies 選項
在 3.4 版更改: 在早期版本中,如果目標目錄已存在,將引發(fā)錯誤,除非使用了 --clear 或 --upgrade 選項。
備注
雖然 Windows 支持符號鏈接,但不推薦使用它們。特別注意,在文件資源管理器中雙擊 python.exe 將立即解析符號鏈接,并忽略虛擬環(huán)境。
備注
在 Microsoft Windows 上,為了啟用 Activate.ps1 腳本,可能需要修改用戶的執(zhí)行策略??梢赃\行以下 PowerShell 命令來執(zhí)行此操作:
PS C:> Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
參閱 About Execution Policies 以獲取更多信息。
生成的 pyvenv.cfg 文件還包括 include-system-site-packages 鍵,如果運行 venv 時帶有 --system-site-packages 選項,則鍵值為 true,否則為 false。
除非采用 --without-pip 選項,否則將會調(diào)用 ensurepip 將 pip 引導到虛擬環(huán)境中。
可以向 venv 傳入多個路徑,此時將根據(jù)給定的選項,在所給的每個路徑上創(chuàng)建相同的虛擬環(huán)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 (* must be replaced by the path to the directory containing the virtual environment):
|
平臺 |
Shell |
用于激活虛擬環(huán)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 上安裝 PowerShell 激活腳本,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. #!/*. 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 適用于Windows的Python啟動器 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
上述的高級方法使用了一個簡單的 API,該 API 提供了一種機制,第三方虛擬環(huán)境創(chuàng)建者可以根據(jù)其需求自定義環(huán)境創(chuàng)建過程,該 API 為 EnvBuilder 類。
class venv.EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False, with_pip=False, prompt=None, upgrade_deps=False)
EnvBuilder 類在實例化時接受以下關鍵字參數(shù):
-
system_site_packages— 一個布爾值,要求系統(tǒng) Python 的 site-packages 對環(huán)境可用(默認為False)。 -
clear— 一個布爾值,如果為 true,則在創(chuàng)建環(huán)境前將刪除目標目錄的現(xiàn)有內(nèi)容。 -
symlinks— 一個布爾值,指示是否嘗試符號鏈接 Python 二進制文件,而不是進行復制。 -
upgrade— 一個布爾值,如果為 true,則將使用當前運行的 Python 去升級一個現(xiàn)有的環(huán)境,這主要在原位置的 Python 更新后使用(默認為False)。 -
with_pip— 一個布爾值,如果為 true,則確保在虛擬環(huán)境中已安裝 pip。這使用的是帶有--default-pip選項的 ensurepip。 -
prompt— 激活虛擬環(huán)境后顯示的提示符(默認為None,表示使用環(huán)境所在的目錄名稱)。如果使用了"."這一特殊字符串,則使用當前目錄的基本名稱作為提示符。 -
upgrade_deps— 將基本 venv 模塊更新為 PyPI 上的最新版本。
在 3.4 版更改: 添加 with_pip 參數(shù)
3.6 新版功能: 添加 prompt 參數(shù)
3.9 新版功能: 添加 upgrade_deps 參數(shù)
第三方虛擬環(huán)境工具的創(chuàng)建者可以自由地將此處提供的 EnvBuilder 類作為基類。
返回的 env-builder 是一個對象,包含一個 create 方法:
-
create(env_dir)
指定要建立虛擬環(huán)境的目標目錄(絕對路徑或相對于當前路徑)來創(chuàng)建虛擬環(huán)境。
create方法將在指定目錄中創(chuàng)建環(huán)境,或者引發(fā)對應的異常。EnvBuilder 類的
create方法定義了可用于定制子類的鉤子: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)
每個方法 ensure_directories(), create_configuration(), setup_python(), setup_scripts() 和 post_setup() 都可以被重寫。
-
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)
在環(huán)境中創(chuàng)建
pyvenv.cfg配置文件。 -
setup_python(context)
在環(huán)境中創(chuàng)建 Python 可執(zhí)行文件的拷貝或符號鏈接。在 POSIX 系統(tǒng)上,如果給定了可執(zhí)行文件
python3.x,將創(chuàng)建指向該可執(zhí)行文件的python和python3符號鏈接,除非相同名稱的文件已經(jīng)存在。 -
setup_scripts(context)
將適用于平臺的激活腳本安裝到虛擬環(huán)境中。
-
upgrade_dependencies(context)
升級環(huán)境中 venv 依賴的核心軟件包(當前為
pip和setuptools)。通過在環(huán)境中使用pip可執(zhí)行文件來完成。3.9 新版功能.
-
post_setup(context)
占位方法,可以在第三方實現(xiàn)中重寫,用于在虛擬環(huán)境中預安裝軟件包,或是其他創(chuàng)建后要執(zhí)行的步驟。
在 3.7.2 版更改: Windows 現(xiàn)在為 python[w].exe 使用重定向腳本,而不是復制實際的二進制文件。僅在 3.7.2 中,除非運行的是源碼樹中的構建,否則 setup_python() 不會執(zhí)行任何操作。
在 3.7.3 版更改: Windows 將重定向腳本復制為 setup_python() 的一部分而非 setup_scripts()。在 3.7.2 中不是這種情況。使用符號鏈接時,將鏈接至原始可執(zhí)行文件。
此外,EnvBuilder 提供了如下實用方法,可以從子類的 setup_scripts() 或 post_setup() 調(diào)用,用來將自定義腳本安裝到虛擬環(huán)境中。
-
install_scripts(context, path)
path 是一個目錄的路徑,該目錄應包含子目錄 “common”, “posix”, “nt”,每個子目錄存有發(fā)往對應環(huán)境中 bin 目錄的腳本。在下列占位符替換完畢后,將復制 “common” 的內(nèi)容和與 os.name 對應的子目錄:
-
__VENV_DIR__會被替換為環(huán)境目錄的絕對路徑。 -
__VENV_NAME__會被替換為環(huán)境名稱(環(huán)境目錄的最后一個字段)。 -
__VENV_PROMPT__會被替換為提示符(用括號括起來的環(huán)境名稱緊跟著一個空格)。 -
__VENV_BIN_NAME__會被替換為 bin 目錄的名稱(bin或Scripts)。 -
__VENV_PYTHON__會被替換為環(huán)境可執(zhí)行文件的絕對路徑。
允許目錄已存在(用于升級現(xiàn)有環(huán)境時)。
-
有一個方便實用的模塊級別的函數(shù):
venv.create(env_dir, system_site_packages=False, clear=False, symlinks=False, with_pip=False, prompt=None, upgrade_deps=False)
通過關鍵詞參數(shù)來創(chuàng)建一個 EnvBuilder,并且使用 env_dir 參數(shù)來調(diào)用它的 create() 方法。
3.3 新版功能.
在 3.4 版更改: 添加 with_pip 參數(shù)
在 3.6 版更改: 添加 prompt 參數(shù)
在 3.9 版更改: 添加 upgrade_deps 參數(shù)
一個擴展 EnvBuilder 的例子
下面的腳本展示了如何通過實現(xiàn)一個子類來擴展 EnvBuilder。這個子類會安裝 setuptools 和 pip 到被創(chuàng)建的虛擬環(huán)境中。
import osimport os.pathfrom subprocess import Popen, PIPEimport sysfrom threading import Threadfrom urllib.parse import urlparsefrom urllib.request import urlretrieveimport venvclass ExtendedEnvBuilder(venv.EnvBuilder):"""This builder installs setuptools and pip so that you can pip oreasy_install other packages into the created virtual environment.:param nodist: If true, setuptools and pip are not installed into thecreated virtual environment.:param nopip: If true, pip is not installed into the createdvirtual environment.:param progress: If setuptools or pip are installed, the progress of theinstallation can be monitored by passing a progresscallable. If specified, it is called with twoarguments: a string indicating some progress, and acontext 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 obtainedby reading lines from the output streams of a subprocesswhich is used to install the app.If a callable is not specified, default progressinformation 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 thevirtual environment being created.:param context: The information for the virtual environmentcreation request being processed."""os.environ['VIRTUAL_ENV'] = context.env_dirif not self.nodist:self.install_setuptools(context)# Can't install pip without setuptoolsif 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 progresscallable (if specified) or write progress information to sys.stderr."""progress = self.progresswhile True:s = stream.readline()if not s:breakif 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_pathdistpath = os.path.join(binpath, fn)# Download script into the virtual environment's binaries folderurlretrieve(url, distpath)progress = self.progressif 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 environmentargs = [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 neededos.unlink(distpath)def install_setuptools(self, context):"""Install setuptools in the virtual environment.:param context: The information for the virtual environmentcreation 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 downloadedpred = 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 environmentcreation request being processed."""url = 'https://bootstrap.pypa.io/get-pip.py'self.install_script(context, 'pip', url)def main(args=None):compatible = Trueif sys.version_info < (3, 3):compatible = Falseelif not hasattr(sys, 'base_prefix'):compatible = Falseif not compatible:raise ValueError('This script is only for use with ''Python 3.3 or later')else:import argparseparser = 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 = Falseelse:use_symlinks = Trueparser.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 = 1try:main()rc = 0except Exception as e:print('Error: %s' % e, file=sys.stderr)sys.exit(rc)
這個腳本同樣可以 在線下載。
文章題目:創(chuàng)新互聯(lián)Python教程:venv—-創(chuàng)建虛擬環(huán)境
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