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:mod:`venv` --- Creation of virtual environments
================================================
.. module:: venv
:synopsis: Creation of virtual environments.
.. moduleauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk>
.. sectionauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk>
.. versionadded:: 3.3
**Source code:** :source:`Lib/venv/`
.. index:: pair: Environments; virtual
--------------
The :mod:`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 (which
matches the version of the binary that was used to create this environment) and
can have its own independent set of installed Python packages in its site
directories.
See :pep:`405` for more information about Python virtual environments.
.. seealso::
`Python Packaging User Guide: Creating and using virtual environments
<https://packaging.python.org/installing/#creating-virtual-environments>`__
.. 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.
Creating virtual environments
-----------------------------
.. include:: /using/venv-create.inc
.. _venv-def:
.. note:: A virtual environment 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 virtual environment is a directory tree which contains Python executable
files and other files which indicate that it is a virtual environment.
Common installation tools such as ``Setuptools`` and ``pip`` work as
expected with virtual environments. In other words, when a virtual
environment is active, they install Python packages into the virtual
environment without needing to be told to do so explicitly.
When a virtual environment is active (i.e., the virtual environment's Python
interpreter is running), the attributes :attr:`sys.prefix` and
:attr:`sys.exec_prefix` point to the base directory of the virtual
environment, whereas :attr:`sys.base_prefix` and
:attr:`sys.base_exec_prefix` point to the non-virtual environment Python
installation which was used to create the virtual environment. If a virtual
environment is not active, then :attr:`sys.prefix` is the same as
:attr:`sys.base_prefix` and :attr:`sys.exec_prefix` is the same as
:attr:`sys.base_exec_prefix` (they all point to a non-virtual environment
Python installation).
When a virtual environment 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 virtual environment active
by running an ``activate`` script in the virtual environment's executables
directory (the precise filename is shell-dependent), which prepends the
virtual environment's directory for executables to the ``PATH`` environment
variable for the running shell. There should be no need in other
circumstances to activate a virtual environment—scripts installed into
virtual environments have a "shebang" line which points to the virtual
environment'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 virtual environment in ``PATH``.
.. _venv-api:
API
---
.. highlight:: python
The high-level method described above makes use of a simple API which provides
mechanisms for third-party virtual environment creators to customize environment
creation according to their needs, the :class:`EnvBuilder` class.
.. class:: EnvBuilder(system_site_packages=False, clear=False, \
symlinks=False, upgrade=False, with_pip=False, \
prompt=None)
The :class:`EnvBuilder` class accepts the following keyword arguments on
instantiation:
* ``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 :mod:`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).
.. versionchanged:: 3.4
Added the ``with_pip`` parameter
.. versionadded:: 3.6
Added the ``prompt`` parameter
Creators of third-party virtual environment tools will be free to use the
provided ``EnvBuilder`` class as a base class.
The returned env-builder is an object which has a method, ``create``:
.. method:: create(env_dir)
This method takes as required argument the path (absolute or relative to
the current directory) of the target directory which is to contain the
virtual environment. The ``create`` method will either create the
environment in the specified directory, or raise an appropriate
exception.
The ``create`` method of the ``EnvBuilder`` class illustrates the hooks
available for subclass customization::
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)
Each of the methods :meth:`ensure_directories`,
:meth:`create_configuration`, :meth:`setup_python`,
:meth:`setup_scripts` and :meth:`post_setup` can be overridden.
.. method:: ensure_directories(env_dir)
Creates the environment directory and all necessary directories, and
returns a context object. This is just a holder for attributes (such as
paths), for use by the other methods. The directories are allowed to
exist already, as long as either ``clear`` or ``upgrade`` were
specified to allow operating on an existing environment directory.
.. method:: create_configuration(context)
Creates the ``pyvenv.cfg`` configuration file in the environment.
.. method:: setup_python(context)
Creates a copy or symlink to the Python executable in the environment.
On POSIX systems, 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.
.. method:: setup_scripts(context)
Installs activation scripts appropriate to the platform into the virtual
environment.
.. method:: post_setup(context)
A placeholder method which can be overridden in third party
implementations to pre-install packages in the virtual environment or
perform other post-creation steps.
.. versionchanged:: 3.7.2
Windows now uses redirector scripts for ``python[w].exe`` instead of
copying the actual binaries. In 3.7.2 only :meth:`setup_python` does
nothing unless running from a build in the source tree.
.. versionchanged:: 3.7.3
Windows copies the redirector scripts as part of :meth:`setup_python`
instead of :meth:`setup_scripts`. This was not the case in 3.7.2.
When using symlinks, the original executables will be linked.
In addition, :class:`EnvBuilder` provides this utility method that can be
called from :meth:`setup_scripts` or :meth:`post_setup` in subclasses to
assist in installing custom scripts into the virtual environment.
.. method:: install_scripts(context, path)
*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 :data:`os.name` are copied after some text
replacement of placeholders:
* ``__VENV_DIR__`` is replaced with the absolute path of the environment
directory.
* ``__VENV_NAME__`` is replaced with the environment name (final path
segment of environment directory).
* ``__VENV_PROMPT__`` is replaced with the prompt (the environment
name surrounded by parentheses and with a following space)
* ``__VENV_BIN_NAME__`` is replaced with the name of the bin directory
(either ``bin`` or ``Scripts``).
* ``__VENV_PYTHON__`` is replaced with the absolute path of the
environment's executable.
The directories are allowed to exist (for when an existing environment
is being upgraded).
There is also a module-level convenience function:
.. function:: create(env_dir, system_site_packages=False, clear=False, \
symlinks=False, with_pip=False, prompt=None)
Create an :class:`EnvBuilder` with the given keyword arguments, and call its
:meth:`~EnvBuilder.create` method with the *env_dir* argument.
.. versionadded:: 3.3
.. versionchanged:: 3.4
Added the ``with_pip`` parameter
.. versionchanged:: 3.6
Added the ``prompt`` parameter
An example of extending ``EnvBuilder``
--------------------------------------
The following script shows how to extend :class:`EnvBuilder` by implementing a
subclass which installs setuptools and pip into a created virtual environment::
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://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 virtual environment.
:param context: The information for the virtual 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 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)
This script is also available for download `online
<https://gist.github.com/vsajip/4673395>`_.