28.3. venv — Création d’environnements virtuels

Nouveau dans la version 3.3.

Code source : Lib/venv/

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The venv module provides support for creating lightweight « virtual environments » with their own site directories, optionally isolated from system site directories. Each virtual environment has its own Python binary (allowing creation of environments with various Python versions) and can have its own independent set of installed Python packages in its site directories.

Voir la PEP 405 pour plus d’informations à propos des environnements virtuels Python.

Note

The pyvenv script has been deprecated as of Python 3.6 in favor of using python3 -m venv to help prevent any potential confusion as to which Python interpreter a virtual environment will be based on.

28.3.1. Création d’environnements virtuels

Creation of virtual environments is done by executing the pyvenv script:

pyvenv /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 the command was run from. It also creates a bin (or Scripts on Windows) subdirectory containing a copy of the python binary (or binaries, in the case of Windows). It also creates an (initially empty) lib/pythonX.Y/site-packages subdirectory (on Windows, this is Lib\site-packages).

Voir aussi

Python Packaging User Guide: Creating and using virtual environments

On Windows, you may have to invoke the pyvenv script as follows, if you don’t have the relevant PATH and PATHEXT settings:

c:\Temp>c:\Python35\python c:\Python35\Tools\Scripts\pyvenv.py myenv

or equivalently:

c:\Temp>c:\Python35\python -m venv myenv

La commande, si lancée avec -h, montrera les options disponibles :

usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
            [--upgrade] [--without-pip]
            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)

Depending on how the venv functionality has been invoked, the usage message may vary slightly, e.g. referencing pyvenv rather than venv.

Modifié dans la version 3.4: Installe pip par défaut, ajout des options --without-pip et --copies

Modifié dans la version 3.4: In earlier versions, if the target directory already existed, an error was raised, unless the --clear or --upgrade option was provided. Now, if an existing directory is specified, its contents are removed and the directory is processed as if it had been newly created.

Le fichier crée pyenv.cfg inclus aussi la clé include-system-site-packages, dont la valeur est true si venv est lancé avec l’option --system-site-packages, sinon sa valeur est false.

Sauf si l’option --without-pip est incluse, ensurepip sera invoqué pour amorcer pip dans l’environnement virtuel.

Multiple paths can be given to pyvenv, in which case an identical virtualenv will be created, according to the given options, at each provided path.

Once a venv has been created, it can be « activated » using a script in the venv’s binary directory. The invocation of the script is platform-specific:

Plateforme	Invite de commande	Commande pour activer l’environnement virtuel
Posix	bash/zsh	$ source <venv>/bin/activate
	fish	$ . <venv>/bin/activate.fish
	csh/tcsh	$ source <venv>/bin/activate.csh
Windows	cmd.exe	C:\\{venv}\\Scripts\\activate.bat
	PowerShell	PS C:\\> <venv>\\Scripts\\Activate.ps1

You don’t specifically need to activate an environment; activation just prepends the venv’s binary directory to your path, so that « python » invokes the venv’s Python interpreter and you can run installed scripts without having to use their full path. However, all scripts installed in a venv should be runnable without activating it, and run with the venv’s Python automatically.

You can deactivate a venv by typing « deactivate » in your shell. The exact mechanism is platform-specific: for example, the Bash activation script defines a « deactivate » function, whereas on Windows there are separate scripts called deactivate.bat and Deactivate.ps1 which are installed when the venv is created.

Nouveau dans la version 3.4: Les scripts d’activation pour fish et csh.

Note

A virtual environment (also called a venv) 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 venv is a directory tree which contains Python executable files and other files which indicate that it is a venv.

Common installation tools such as Setuptools and pip work as expected with venvs - i.e. when a venv is active, they install Python packages into the venv without needing to be told to do so explicitly.

When a venv is active (i.e. the venv’s Python interpreter is running), the attributes sys.prefix and sys.exec_prefix point to the base directory of the venv, whereas sys.base_prefix and sys.base_exec_prefix point to the non-venv Python installation which was used to create the venv. If a venv 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-venv Python installation).

When a venv 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 venv active by running an activate script in the venv’s executables directory (the precise filename is shell-dependent), which prepends the venv’s directory for executables to the PATH environment variable for the running shell. There should be no need in other circumstances to activate a venv – scripts installed into venvs have a shebang line which points to the venv’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 venv in PATH.

28.3.2. API

La méthode haut niveau décrite au dessus utilise une API simple qui permet à des créateurs d’environnements virtuels externes de personnaliser la création d’environnements virtuels basés sur leurs besoins, la classe EnvBuilder.

class venv.EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False, with_pip=False)

La classe EnvBuilder accepte les arguments suivants lors de l’instanciation :

• system_site_packages – Une valeur booléenne qui indique que les site-packages du système Python devraient être disponibles dans l’environnement virtuel (par défaut à False).
• clear – Une valeur booléenne qui, si vraie, supprimera le contenu de n’importe quel dossier existant cible, avant de créer l’environnement.
• symlinks – a Boolean value indicating whether to attempt to symlink the Python binary (and any necessary DLLs or other binaries, e.g. pythonw.exe), rather than copying. Defaults to True on Linux and Unix systems, but False on Windows.
• upgrade – Une valeur booléenne qui, si vraie, mettra à jour un environnement existant avec le Python lancé – utilisé quand Python à été mis a jour sur place (par défaut à False).
• with_pip – Une valeur booléenne qui, si vraie, assure que pip est installé dans l’environnement virtuel. Cela utilise ensurepip avec l’option --default-pip.

Modifié dans la version 3.4: Ajout du paramètre with_pip

Les créateurs des outils de création d’environnement virtuel externes seront libres d’utiliser la classe EnvBuilder en tant que classe de base.

Le env-builder retourné est un objet qui a une méthode, create :

create(env_dir)

Cette méthode prends en argument obligatoire le chemin (absolu ou relatif par rapport au dossier courant) du dossier cible qui doit contenir l’environnement virtuel. La méthode create doit soit créer un environnement dans le dossier spécifié, soit lever une exception.

La méthode create de la classe EnvBuilder illustre les points d’entrées disponibles pour la personnalisation de sous-classes :

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)

Chacune des méthodes ensure_directories(), create_configuration(), setup_python(), setup_scripts() et post_setup() peuvent être écrasés.

ensure_directories(env_dir)

Crée un dossier d’environnement et tous les dossiers nécessaires, et retourne un objet contexte. C’est juste un conteneur pour des attributs (comme des chemins), qui sera utilisé par d’autres méthodes. Ces dossiers peuvent déjà exister. tant que clear ou upgrade ont été spécifiés pour permettre de telles opérations dans un dossier d’environnement existant.

create_configuration(context)

Crée le fichier de configuration pyenv.cfg dans l’environnement.

setup_python(context)

Creates a copy of the Python executable (and, under Windows, DLLs) in the environment. On a POSIX system, 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)

Installe les scripts d’activation appropriés à la plateforme dans l’environnement virtuel.

post_setup(context)

Une méthode qui n’est la que pour se faire surcharger dans des implémentation externes pour pré installer des paquets dans l’environnement virtuel ou pour exécuter des étapes post-création.

De plus, EnvBuilder propose cette méthode utilitaire qui peut être appelée de setup_scripts() ou post_setup() dans des sous classes pour assister dans l’installation de scripts customs dans l’environnement virtuel.

install_scripts(context, path)

path corresponds au chemin vers le dossier qui contiens les sous dossiers « common », « posix », « nt », chacun contenant des scripts destinés pour le dossier « bin » dans l’environnement. Le contenu du dossier « common » et le dossier correspondant à os.name sont copiés après quelque remplacement de texte temporaires :

• __VENV_DIR__ est remplacé avec le chemin absolu du dossier de l’environnement.
• __VENV_NAME__ est remplacé avec le nom de l’environnement (le dernier segment du chemin vers le dossier de l’environnement).
• __VENV_PROMPT__ est remplacé par le prompt (nom de l’environnement entouré de parenthèses et avec un espace le suivant).
• __VENV_BIN_NAME__ est remplacé par le nom du dossier bin (soit bin soit Scripts).
• __VENV_PYTHON__ est remplacé avec le chemin absolu de l’exécutable de l’environnement.

Les dossiers peuvent exister (pour quand un environnement existant est mis à jour).

Il y a aussi une fonction pratique au niveau du module :

venv.create(env_dir, system_site_packages=False, clear=False, symlinks=False, with_pip=False)

Crée une EnvBuilder avec les arguments donnés, et appelle sa méthode create() avec l’argument env_dir.

Modifié dans la version 3.4: Ajout du paramètre with_pip

28.3.3. Un exemple d’extension de EnvBuilder

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

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 environment.

    :param nodist: If True, setuptools and pip are not installed into the
                   created environment.
    :param nopip: If True, pip is not installed into the created
                  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
        environment being created.

        :param context: The information for the 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 env'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 env
        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 environment.

        :param context: The information for the 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 environment.

        :param context: The information for the environment creation request
                        being processed.
        """
        url = 'https://raw.github.com/pypa/pip/master/contrib/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 to create the environment in.')
        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 '
                                               'environment directory if it '
                                               'already exists, before '
                                               'environment creation.')
        parser.add_argument('--upgrade', default=False, action='store_true',
                            dest='upgrade', help='Upgrade the 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.