"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 by default is isolated from
the packages in the base environment, so that 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.

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

ENV_DIR

   A required argument specifying the directory to create the
   environment in.

--system-site-packages

   Give the virtual environment access to the system site-packages
   directory.

--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).

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 pour activer l'environnement virtuel      |
|               | commande     |                                                    |
|===============|==============|====================================================|
| 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.
