: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:: 3.3Source code: :source:`Lib/venv/`
.. index:: pair: Environments; virtualThe :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 (allowing creation of environments with various Python versions) 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.
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.
Note
A virtual environment (also called a venv) is a Python
environment such that the Python interpreter, libraries and scripts
installed into it are isolated from those installed in other virtual
environments, and (by default) any libraries installed in a "system" Python,
i.e. one which is installed as part of your operating system.
A venv is a directory tree which contains Python executable files and other files which indicate that it is a venv.
Common installation tools such as Setuptools and pip work as
expected with venvs - i.e. when a venv is active, they install Python
packages into the venv without needing to be told to do so explicitly.
When a venv is active (i.e. the venv's Python interpreter is running), the attributes :attr:`sys.prefix` and :attr:`sys.exec_prefix` point to the base directory of the venv, whereas :attr:`sys.base_prefix` and :attr:`sys.base_exec_prefix` point to the non-venv Python installation which was used to create the venv. If a venv is not active, then :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-venv Python installation).
When a venv is active, any options that change the installation path will be ignored from all distutils configuration files to prevent projects being inadvertently installed outside of the virtual environment.
When working in a command shell, users can make a venv active by running an
activate script in the venv's executables directory (the precise filename
is shell-dependent), which prepends the venv's directory for executables to
the PATH environment variable for the running shell. There should be no
need in other circumstances to activate a venv -- scripts installed into
venvs have a shebang line which points to the venv's Python interpreter. This
means that the script will run with that interpreter regardless of the value
of PATH. On Windows, shebang line processing is supported if you have the
Python Launcher for Windows installed (this was added to Python in 3.3 - see
PEP 397 for more details). Thus, double-clicking an installed script in
a Windows Explorer window should run the script with the correct interpreter
without there needing to be any reference to its venv in PATH.
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.
There is also a module-level convenience function:
.. function:: create(env_dir, system_site_packages=False, clear=False, \
symlinks=False, with_pip=False)
Create an :class:`EnvBuilder` with the given keyword arguments, and call its
:meth:`~EnvBuilder.create` method with the *env_dir* argument.
.. versionchanged:: 3.4
Added the ``with_pip`` parameterThe following script shows how to extend :class:`EnvBuilder` by implementing a subclass which installs setuptools and pip into a created venv:
import os
import os.path
from subprocess import Popen, PIPE
import sys
from threading import Thread
from urllib.parse import urlparse
from urllib.request import urlretrieve
import venv
class ExtendedEnvBuilder(venv.EnvBuilder):
"""
This builder installs setuptools and pip so that you can pip or
easy_install other packages into the created environment.
:param nodist: If True, setuptools and pip are not installed into the
created environment.
:param nopip: If True, pip is not installed into the created
environment.
:param progress: If setuptools or pip are installed, the progress of the
installation can be monitored by passing a progress
callable. If specified, it is called with two
arguments: a string indicating some progress, and a
context indicating where the string is coming from.
The context argument can have one of three values:
'main', indicating that it is called from virtualize()
itself, and 'stdout' and 'stderr', which are obtained
by reading lines from the output streams of a subprocess
which is used to install the app.
If a callable is not specified, default progress
information is output to sys.stderr.
"""
def __init__(self, *args, **kwargs):
self.nodist = kwargs.pop('nodist', False)
self.nopip = kwargs.pop('nopip', False)
self.progress = kwargs.pop('progress', None)
self.verbose = kwargs.pop('verbose', False)
super().__init__(*args, **kwargs)
def post_setup(self, context):
"""
Set up any packages which need to be pre-installed into the
environment being created.
:param context: The information for the environment creation request
being processed.
"""
os.environ['VIRTUAL_ENV'] = context.env_dir
if not self.nodist:
self.install_setuptools(context)
# Can't install pip without setuptools
if not self.nopip and not self.nodist:
self.install_pip(context)
def reader(self, stream, context):
"""
Read lines from a subprocess' output stream and either pass to a progress
callable (if specified) or write progress information to sys.stderr.
"""
progress = self.progress
while True:
s = stream.readline()
if not s:
break
if progress is not None:
progress(s, context)
else:
if not self.verbose:
sys.stderr.write('.')
else:
sys.stderr.write(s.decode('utf-8'))
sys.stderr.flush()
stream.close()
def install_script(self, context, name, url):
_, _, path, _, _, _ = urlparse(url)
fn = os.path.split(path)[-1]
binpath = context.bin_path
distpath = os.path.join(binpath, fn)
# Download script into the env's binaries folder
urlretrieve(url, distpath)
progress = self.progress
if self.verbose:
term = '\n'
else:
term = ''
if progress is not None:
progress('Installing %s ...%s' % (name, term), 'main')
else:
sys.stderr.write('Installing %s ...%s' % (name, term))
sys.stderr.flush()
# Install in the env
args = [context.env_exe, fn]
p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
t1.start()
t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
t2.start()
p.wait()
t1.join()
t2.join()
if progress is not None:
progress('done.', 'main')
else:
sys.stderr.write('done.\n')
# Clean up - no longer needed
os.unlink(distpath)
def install_setuptools(self, context):
"""
Install setuptools in the environment.
:param context: The information for the environment creation request
being processed.
"""
url = 'https://bitbucket.org/pypa/setuptools/downloads/ez_setup.py'
self.install_script(context, 'setuptools', url)
# clear up the setuptools archive which gets downloaded
pred = lambda o: o.startswith('setuptools-') and o.endswith('.tar.gz')
files = filter(pred, os.listdir(context.bin_path))
for f in files:
f = os.path.join(context.bin_path, f)
os.unlink(f)
def install_pip(self, context):
"""
Install pip in the environment.
:param context: The information for the environment creation request
being processed.
"""
url = 'https://raw.github.com/pypa/pip/master/contrib/get-pip.py'
self.install_script(context, 'pip', url)
def main(args=None):
compatible = True
if sys.version_info < (3, 3):
compatible = False
elif not hasattr(sys, 'base_prefix'):
compatible = False
if not compatible:
raise ValueError('This script is only for use with '
'Python 3.3 or later')
else:
import argparse
parser = argparse.ArgumentParser(prog=__name__,
description='Creates virtual Python '
'environments in one or '
'more target '
'directories.')
parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
help='A directory to create the environment in.')
parser.add_argument('--no-setuptools', default=False,
action='store_true', dest='nodist',
help="Don't install setuptools or pip in the "
"virtual environment.")
parser.add_argument('--no-pip', default=False,
action='store_true', dest='nopip',
help="Don't install pip in the virtual "
"environment.")
parser.add_argument('--system-site-packages', default=False,
action='store_true', dest='system_site',
help='Give the virtual environment access to the '
'system site-packages dir.')
if os.name == 'nt':
use_symlinks = False
else:
use_symlinks = True
parser.add_argument('--symlinks', default=use_symlinks,
action='store_true', dest='symlinks',
help='Try to use symlinks rather than copies, '
'when symlinks are not the default for '
'the platform.')
parser.add_argument('--clear', default=False, action='store_true',
dest='clear', help='Delete the contents of the '
'environment directory if it '
'already exists, before '
'environment creation.')
parser.add_argument('--upgrade', default=False, action='store_true',
dest='upgrade', help='Upgrade the environment '
'directory to use this version '
'of Python, assuming Python '
'has been upgraded in-place.')
parser.add_argument('--verbose', default=False, action='store_true',
dest='verbose', help='Display the output '
'from the scripts which '
'install setuptools and pip.')
options = parser.parse_args(args)
if options.upgrade and options.clear:
raise ValueError('you cannot supply --upgrade and --clear together.')
builder = ExtendedEnvBuilder(system_site_packages=options.system_site,
clear=options.clear,
symlinks=options.symlinks,
upgrade=options.upgrade,
nodist=options.nodist,
nopip=options.nopip,
verbose=options.verbose)
for d in options.dirs:
builder.create(d)
if __name__ == '__main__':
rc = 1
try:
main()
rc = 0
except Exception as e:
print('Error: %s' % e, file=sys.stderr)
sys.exit(rc)This script is also available for download online.