# `venv` — Creation of virtual environments

Added in version 3.3.

Código fuente: 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.

Ver PEP 405 para más información sobre los entornos virtuales de Python.

Ver también

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.

## Creación de entornos virtuales

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 `Lib\site-packages`). If an existing directory is specified, it will be re-used.

Distinto en la versión 3.5: The use of `venv` is now recommended for creating virtual environments.

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

The command, if run with `-h`, will show the available options:

    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).

Distinto en la versión 3.4: Installs pip by default, added the `--without-pip` and `--copies` options.

Distinto en la versión 3.4: In earlier versions, if the target directory already existed, an error was raised, unless the `--clear` or `--upgrade` option was provided.

Distinto en la versión 3.9: Add `--upgrade-deps` option to upgrade pip + setuptools to the latest on PyPI.

Distinto en la versión 3.12: `setuptools` is no longer a core venv dependency.

Distinto en la versión 3.13: Added the `--without-scm-ignore-files` option.

Distinto en la versión 3.13: `venv` now creates a `.gitignore` file for Git by default.

Nota

While symlinks are supported on Windows, they are not recommended. Of particular note is that double-clicking `python.exe` in File Explorer will resolve the symlink eagerly and ignore the virtual environment.

Nota

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.

Unless the `--without-pip` option is given, `ensurepip` will be invoked to bootstrap `pip` into the virtual environment.

Multiple paths can be given to `venv`, in which case an identical virtual environment will be created, according to the given options, at each provided path.

## Cómo funcionan los venvs

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):

Plataforma | Shell | Comando para activar el entorno virtual
--- | --- | ---
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`

Added in version 3.4: fish and csh activation scripts.

Added in version 3.8: Scripts de activación de PowerShell instalados en POSIX para compatibilidad con PowerShell Core.

No necesita específicamente activar un entorno virtual, ya que puede solo especificar la ruta completa al intérprete de Python de ese entorno al invocar Python. Además, todos los scripts instalados en el entorno deben poder ejecutarse sin activarlo.

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 Lanzador de Python para 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`.

Cuando se ha activado un entorno virtual, la variable de entorno `VIRTUAL_ENV` se establece en la ruta del entorno. Dado que no se requiere activar explícitamente una entorno virtual para usarla, no se puede confiar en `VIRTUAL_ENV` para determinar si se está usando un entorno virtual.

Advertencia

Debido a que los scripts instalados en entornos no deben esperar a que el entorno se active, sus líneas shebang contienen las rutas absolutas a los intérpretes de su entorno. Debido a esto, los entornos son inherentemente no portables, en el caso general. Siempre debe tener un medio simple para recrear un entorno (por ejemplo, si tiene un archivo de requisitos `requirements.txt`, puede invocar `pip install -r requirements.txt` al usar `pip` del entorno para instalar todos los paquetes que necesite el entorno). Si por alguna razón necesita mover el entorno a una nueva ubicación, debe recrearlo en la ubicación deseada y eliminar el de la ubicación anterior. Si mueve un entorno porque movió un directorio principal del mismo, debe recrear el entorno en su nueva ubicación. De lo contrario, el software instalado en el entorno puede no funcionar como se espera.

Puede desactivar un entorno virtual al escribir `deactivate` en el shell. El mecanismo exacto es específico de la plataforma y es un detalle de implementación interno (se usará normalmente una función de script o shell).

## API

El método de alto nivel descrito anteriormente utiliza una sencilla API que proporciona mecanismos para que les creadores de entornos virtuales de terceras/os puedan personalizar la creación de entornos según sus necesidades, la clase `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 clase `EnvBuilder` acepta los siguientes argumentos de palabras clave en la instanciación:

  - 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()`.

  Distinto en la versión 3.4: Añadido el parámetro `with_pip`

  Distinto en la versión 3.6: Añadido el parámetro `prompt`

  Distinto en la versión 3.9: Se agregó el parámetro `upgrade_deps`

  Distinto en la versión 3.13: Added the `scm_ignore_files` parameter

  `EnvBuilder` may be used as a base class.

  create(env_dir)

    Crear un entorno virtual especificando el directorio de destino (de forma absoluta o relativa al directorio actual) que ha de contener el entorno virtual. El método `create` creará el entorno en el directorio especificado, o lanzará la correspondiente excepción.

    El método `create` de la clase `EnvBuilder` ilustra los enlaces disponibles para la personalización de la subclase:

        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)

    Cada uno de los métodos `ensure_directories()`, `create_configuration()`, `setup_python()`, `setup_scripts()` y `post_setup()` pueden ser anulados.

  ensure_directories(env_dir)

    Crea el directorio del entorno y todos los subdirectorios necesarios que aún no existen, y retorna un objeto de contexto. Este objeto de contexto es solo un contenedor de atributos (como rutas) para que lo usen otros métodos. Si se crea `EnvBuilder` con el argumento `clear=True`, se borrará el contenido del directorio del entorno y luego se recrearán todos los subdirectorios necesarios.

    El objeto de contexto que retorna es un `types.SimpleNamespace` con los siguientes atributos:

    - `env_dir` - La ubicación del entorno virtual. Se usa para `__VENV_DIR__` en scripts de activación (ver `install_scripts()`).

    - `env_name` - El nombre del entorno virtual. Se usa para `__VENV_NAME__` en scripts de activación (ver `install_scripts()`).

    - `prompt` - El prompt que utilizarán los scripts de activación. Se usa para `__VENV_PROMPT__` en scripts de activación (ver `install_scripts()`).

    - `executable` - El ejecutable de Python subyacente que se utiliza por el entorno virtual. Esto tiene en cuenta el caso donde se crea un entorno virtual a partir de otro entorno virtual.

    - `inc_path` - La ruta de include para el entorno virtual.

    - `lib_path` - La ruta de purelib para el entorno virtual.

    - `bin_path` - La ruta del script para el entorno virtual.

    - `bin_name` - El nombre de la ruta del script en relación con la ubicación del entorno virtual. Se usa para `__VENV_BIN_NAME__` en scripts de activación (ver `install_scripts()`).

    - `env_exe` - El nombre del intérprete de Python en el entorno virtual. Se usa para `__VENV_PYTHON__` en scripts de activación (ver `install_scripts()`).

    - `env_exec_cmd` - El nombre del intérprete de Python, teniendo en cuenta las redirecciones del sistema de archivos. Se puede utilizar para ejecutar Python en el entorno virtual.

    Distinto en la versión 3.11: El esquema de instalación de sysconfig de venv se utiliza para construir las rutas de los directorios creados.

    Distinto en la versión 3.12: Se agregó el atributo `lib_path` al contexto y se documentó el objeto de contexto.

  create_configuration(context)

    Crea el archivo de configuración `pyvenv.cfg` en el entorno.

  setup_python(context)

    Crea una copia o enlace simbólico al ejecutable Python en el entorno. En los sistemas POSIX, si se usó un ejecutable específico `python3.x`, se crearán enlaces simbólicos a `python` y `python3` apuntando a ese ejecutable, a menos que ya existan archivos con esos nombres.

  setup_scripts(context)

    Instala los scripts de activación apropiados para la plataforma en el entorno virtual.

  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.

    Added in version 3.9.

    Distinto en la versión 3.12: setuptools is no longer a core venv dependency.

  post_setup(context)

    Un método de marcador de posición que puede ser anulado en implementaciones de terceros/as para previo instalar paquetes en el entorno virtual o realizar otros pasos posteriores a la creación.

  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__` se sustituye por la ruta absoluta del directorio del entorno.

    - `__VENV_NAME__` se sustituye por el nombre del entorno (parte final de la ruta del directorio del entorno).

    - `__VENV_PROMPT__` se sustituye por el prompt (el nombre del entorno entre paréntesis y con un espacio posterior)

    - `__VENV_BIN_NAME__` se sustituye con el nombre del directorio bin (ya sea `bin` o `Scripts`).

    - `__VENV_PYTHON__` se sustituye con la ruta absoluta del ejecutable del entorno.

    Se permite la existencia de los directorios (para cuando se está actualizando un entorno existente).

  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.

    Added in version 3.13.

  Distinto en la versión 3.7.2: Windows ahora usa scripts de redireccionamiento para `python[w].exe` en lugar de copiar los propios binarios. Para 3.7.2 solamente `setup_python()` no hace nada a menos que se ejecute desde una compilación en el árbol de directorios fuente.

  Distinto en la versión 3.7.3: Windows copia los scripts de redireccionamiento como parte de `setup_python()` en lugar de `setup_scripts()`. Este no era el caso para 3.7.2. Cuando se usan enlaces simbólicos, los ejecutables originales se enlazan.

También hay una función de conveniencia a nivel de módulo:

venv.create(env_dir, system_site_packages=False, clear=False, symlinks=False, with_pip=False, prompt=None, upgrade_deps=False, *, scm_ignore_files=frozenset())

  Crea un `EnvBuilder` con los argumentos de la palabra clave dada, y llama a su método `create()` con el argumento env_dir.

  Added in version 3.3.

  Distinto en la versión 3.4: Added the with_pip parameter

  Distinto en la versión 3.6: Added the prompt parameter

  Distinto en la versión 3.9: Added the upgrade_deps parameter

  Distinto en la versión 3.13: Added the scm_ignore_files parameter

## Un ejemplo de la extensión de `EnvBuilder`

El siguiente script muestra como extender `EnvBuilder` implementando una subclase que instala setuptools y pip en un entorno virtual creado:

    import os
    import os.path
    from subprocess import Popen, PIPE
    import sys
    from threading import Thread
    from urllib.parse import urlsplit
    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, _, _ = urlsplit(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)

Este script está también disponible para su descarga online.