# `venv` --- Creation of virtual environments

Ajouté dans la version 3.3.

Code source : 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.

A virtual environment is (amongst other things):

- Used to contain a specific Python interpreter and software libraries and binaries which are needed to support a project (library or application). These are by default isolated from software in other virtual environments and Python interpreters and libraries installed in the operating system.

- Contained in a directory, conventionally named `.venv` or `venv` in the project directory, or under a container directory for lots of virtual environments, such as `~/.virtualenvs`.

- Not checked into source control systems such as Git.

- Considered as disposable -- it should be simple to delete and recreate it from scratch. You don't place any project code in the environment.

- Not considered as movable or copyable -- you just recreate the same environment in the target location.

See PEP 405 for more background on Python virtual environments.

Voir aussi

Python Packaging User Guide: Creating and using virtual environments

Availability: not Android, not iOS, not WASI.

This module is not supported on mobile platforms or WebAssembly platforms.

## Création d'environnements virtuels

Virtual environments are created by executing the `venv` module:

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

This creates the target directory (including parent directories as needed) and places a `pyvenv.cfg` file in it with a `home` key pointing to the Python installation from which the command was run. It also creates a `bin` (or `Scripts` on Windows) subdirectory containing a copy or symlink of the Python executable (as appropriate for the platform or arguments used at environment creation time). It also creates a `lib/pythonX.Y/site-packages` subdirectory (on Windows, this is `Libsite-packages`). If an existing directory is specified, it will be re-used.

Modifié dans la version 3.5: L'utilisation de `venv` est maintenant recommandée pour créer vos environnements virtuels.

Deprecated since version 3.6, removed in version 3.8: pyvenv was the recommended tool for creating virtual environments for Python 3.3 and 3.4, and replaced in 3.5 by executing `venv` directly.

On Windows, invoke the `venv` command as follows:

    PS> python -m venv C:\path\to\new\virtual\environment

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

    usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
                [--upgrade] [--without-pip] [--prompt PROMPT] [--upgrade-deps]
                [--without-scm-ignore-files]
                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.

    options:
      -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) to the latest
                            version in PyPI
      --without-scm-ignore-files
                            Skips adding SCM ignore files to the environment
                            directory (Git is supported by default).

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

Modifié dans la version 3.4: Installs pip by default, added the `--without-pip` and `--copies` options.

Modifié dans la version 3.4: Dans les versions précédentes, si le dossier de destination existait déjà, une erreur était levée, sauf si l'option `--clear` ou `--upgrade` était incluse.

Modifié dans la version 3.9: Add `--upgrade-deps` option to upgrade pip + setuptools to the latest on PyPI.

Modifié dans la version 3.12: `setuptools` is no longer a core venv dependency.

Modifié dans la version 3.13: Added the `--without-scm-ignore-files` option.

Modifié dans la version 3.13: `venv` now creates a `.gitignore` file for Git by default.

Note

Bien que les liens symboliques soient pris en charge sous Windows, ils ne sont pas recommandés. Il est particulièrement à noter que le double-clic sur `python.exe` dans l'Explorateur de fichiers suivra le lien symbolique et ignorera l'environnement virtuel.

Note

On Microsoft Windows, it may be required to enable the `Activate.ps1` script by setting the execution policy for the user. You can do this by issuing the following PowerShell command:

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

See About Execution Policies for more information.

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.

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

Plusieurs chemins peuvent être donnés à `venv`, et dans ce cas un environnement virtuel sera créé, en fonction des options incluses, à chaque chemin donné.

## 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):

Plateforme | Invite de commande | Commande pour activer l'environnement virtuel
--- | --- | ---
POSIX | bash/zsh | `$ source <venv>/bin/activate`
fish | `$ source <venv>/bin/activate.fish`
csh/tcsh | `$ source <venv>/bin/activate.csh`
pwsh | `$ <venv>/bin/Activate.ps1`
Windows | cmd.exe | `C:\> <venv>\Scripts\activate.bat`
PowerShell | `PS C:\> <venv>\Scripts\Activate.ps1`

Ajouté dans la version 3.4: fish and csh activation scripts.

Ajouté dans la version 3.8: Scripts d'activation PowerShell installés sous POSIX pour le support de 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, `#!/<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 Lanceur Python pour Windows 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.

Avertissement

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

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, prompt=None, upgrade_deps=False, *, scm_ignore_files=frozenset())

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

  - 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

  - scm_ignore_files -- Create ignore files based for the specified source control managers (SCM) in the iterable. Support is defined by having a method named `create_{scm}_ignore_file`. The only value supported by default is `"git"` via `create_git_ignore_file()`.

  Modifié dans la version 3.4: Ajout du paramètre `with_pip`

  Modifié dans la version 3.6: Ajout du paramètre `prompt`

  Modifié dans la version 3.9: Added the `upgrade_deps` parameter

  Modifié dans la version 3.13: Added the `scm_ignore_files` parameter

  `EnvBuilder` may be used as a base class.

  create(env_dir)

    Crée un environnement virtuel en spécifiant le chemin cible (absolu ou relatif par rapport au dossier courant) qui contiendra l'environnement virtuel. La méthode `create` crée l'environnement dans le dossier spécifié ou lève une exception appropriée.

    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)

    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.

    Modifié dans la version 3.11: The venv sysconfig installation scheme is used to construct the paths of the created directories.

    Modifié dans la version 3.12: The attribute `lib_path` was added to the context, and the context object was documented.

  create_configuration(context)

    Crée le fichier de configuration `pyvenv.cfg` dans l'environnement.

  setup_python(context)

    Crée une copie ou un lien symbolique vers l'exécutable Python dans l'environnement. Sur les systèmes POSIX, si un exécutable spécifique `python3.x` a été utilisé, des liens symboliques vers `python` et `python3` seront créés pointant vers cet exécutable, sauf si des fichiers avec ces noms existent déjà.

  setup_scripts(context)

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

  upgrade_dependencies(context)

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

    Ajouté dans la version 3.9.

    Modifié dans la version 3.12: setuptools is no longer a core venv dependency.

  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.

  install_scripts(context, path)

    This method can be called from `setup_scripts()` or `post_setup()` in subclasses to assist in installing custom scripts into the virtual environment.

    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__` 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).

  create_git_ignore_file(context)

    Creates a `.gitignore` file within the virtual environment that causes the entire directory to be ignored by the Git source control manager.

    Ajouté dans la version 3.13.

  Modifié dans la version 3.7.2: Windows utilise maintenant des scripts de redirection pour `python[w].exe` au lieu de copier les fichiers binaires. En 3.7.2 seulement `setup_python()` ne fait rien sauf s'il s'exécute à partir d'un build dans l'arborescence source.

  Modifié dans la version 3.7.3: Windows copie les scripts de redirection dans le cadre de `setup_python()` au lieu de `setup_scripts()`. Ce n'était pas le cas en 3.7.2. Lorsque vous utilisez des liens symboliques, les exécutables originaux seront liés.

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, prompt=None, upgrade_deps=False, *, scm_ignore_files=frozenset())

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

  Ajouté dans la version 3.3.

  Modifié dans la version 3.4: Added the with_pip parameter

  Modifié dans la version 3.6: Added the prompt parameter

  Modifié dans la version 3.9: Added the upgrade_deps parameter

  Modifié dans la version 3.13: Added the scm_ignore_files parameter

## Un exemple d'extension de `EnvBuilder`

Le script qui suis montre comment étendre `EnvBuilder` en implémentant une sous-classe qui installe setuptools et pip dans un environnement créé :

    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://bootstrap.pypa.io/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):
        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)

Ce script est aussi disponible au téléchargement en ligne.