:mod:`!venv` --- Creation of virtual environments
.. module:: venv :synopsis: Creationofvirtualenvironments... moduleauthor:: VinaySajip<vinay_sajip@yahoo.co.uk>.. sectionauthor:: VinaySajip<vinay_sajip@yahoo.co.uk>.. versionadded:: 3.3Source code::source:`Lib/venv/`
.. index:: pair: Environments; virtualThe :mod:`!venv` module supports creating lightweight "virtual environments", each with their own independent set of Python packages installed in their :mod:`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. See :ref:`sys-path-init-virtual-environments` and :mod:`site`'s :ref:`virtual environments documentation <site-virtual-environments-configuration>` for more information.
When used from within a virtual environment, common installation tools such as :pypi:`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
.venvorvenvin 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.
.. seealso:: `PythonPackagingUserGuide: Creatingandusingvirtualenvironments<https://packaging.python.org/guides/installing-using-pip-and-virtual-environments/#create-and-use-virtual-environments>`__:ref:`Virtual environments <venv-def>` are created by executing the venv module:
python -m venv /path/to/new/virtual/environmentThis creates the target directory (including parent directories as needed) and places a :file:`pyvenv.cfg` file in it with a home key pointing to the Python installation from which the command was run. It also creates a :file:`bin` (or :file:`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 :file:`lib/pythonX.Y/site-packages` subdirectory (on Windows, this is :file:`Lib\site-packages`). If an existing directory is specified, it will be re-used.
.. versionchanged:: 3.5Theuseof``venv``isnowrecommendedforcreatingvirtualenvironments... deprecated-removed:: 3.63.8 :program:`pyvenv`wastherecommendedtoolforcreatingvirtualenvironmentsforPython3.3and3.4, andreplacedin3.5byexecuting``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] [--promptPROMPT] [--upgrade-deps] [--without-scm-ignore-files] ENV_DIR [ENV_DIR ...] CreatesvirtualPythonenvironmentsinoneormoretargetdirectories. positionalarguments: ENV_DIRAdirectorytocreatetheenvironmentin. options: -h, --helpshowthishelpmessageandexit--system-site-packagesGivethevirtualenvironmentaccesstothesystemsite-packagesdir. --symlinksTrytousesymlinksratherthancopies, whensymlinksarenotthedefaultfortheplatform. --copiesTrytousecopiesratherthansymlinks, evenwhensymlinksarethedefaultfortheplatform. --clearDeletethecontentsoftheenvironmentdirectoryifitalreadyexists, beforeenvironmentcreation. --upgradeUpgradetheenvironmentdirectorytousethisversionofPython, assumingPythonhasbeenupgradedin-place. --without-pipSkipsinstallingorupgradingpipinthevirtualenvironment (pipisbootstrappedbydefault) --promptPROMPTProvidesanalternativepromptprefixforthisenvironment. --upgrade-depsUpgradecoredependencies (pip) tothelatestversioninPyPI--without-scm-ignore-filesSkipsaddingSCMignorefilestotheenvironmentdirectory (Gitissupportedbydefault). Onceanenvironmenthasbeencreated, youmaywishtoactivateit, e.g. bysourcinganactivatescriptinitsbindirectory... versionchanged:: 3.4Installspipbydefault, addedthe``--without-pip``and``--copies``options... versionchanged:: 3.4Inearlierversions, ifthetargetdirectoryalreadyexisted, anerrorwasraised, unlessthe``--clear``or``--upgrade``optionwasprovided... versionchanged:: 3.9Add``--upgrade-deps``optiontoupgradepip+setuptoolstothelatestonPyPI... versionchanged:: 3.12``setuptools``isnolongeracorevenvdependency... versionchanged:: 3.13Addedthe``--without-scm-ignore-files``option... versionchanged:: 3.13``venv``nowcreatesa :file:`.gitignore`fileforGitbydefault.Note
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.
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 CurrentUserSee About Execution Policies for more information.
The created :file:`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, :mod:`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.
When a Python interpreter is running from a virtual environment, :data:`sys.prefix` and :data:`sys.exec_prefix` point to the directories of the virtual environment, whereas :data:`sys.base_prefix` and :data:`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 :envvar:`PATH`, so that running :program:`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 (:samp:`{<venv>}` must be replaced by the path to the directory containing the virtual environment):
| Platform | Shell | Command to activate virtual environment |
|---|---|---|
| POSIX | bash/zsh | :samp:`$ source {<venv>}/bin/activate` |
| fish | :samp:`$ source {<venv>}/bin/activate.fish` | |
| csh/tcsh | :samp:`$ source {<venv>}/bin/activate.csh` | |
| pwsh | :samp:`$ {<venv>}/bin/Activate.ps1` | |
| Windows | cmd.exe | :samp:`C:\\> {<venv>}\\Scripts\\activate.bat` |
| PowerShell | :samp:`PS C:\\> {<venv>}\\Scripts\\Activate.ps1` |
.. versionadded:: 3.4 :program:`fish`and :program:`csh`activationscripts... versionadded:: 3.8PowerShellactivationscriptsinstalledunderPOSIXforPowerShellCoresupport.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, :samp:`#!/{<path-to-venv>}/bin/python`. This means that the script will run with that interpreter regardless of the value of :envvar:`PATH`. On Windows, "shebang" line processing is supported if you have the :ref:`launcher` 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 :envvar:`PATH`.
When a virtual environment has been activated, the :envvar:`!VIRTUAL_ENV` environment variable is set to the path of the environment. Since explicitly activating a virtual environment is not required to use it, :envvar:`!VIRTUAL_ENV` cannot be relied upon to determine whether a virtual environment is being used.
Warning
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).
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, prompt=None, \ upgrade_deps=False, *, scm_ignore_files=frozenset()) Createan :class:`EnvBuilder`withthegivenkeywordarguments, andcallits :meth:`~EnvBuilder.create`methodwiththe*env_dir*argument. .. versionadded:: 3.3 .. versionchanged:: 3.4Addedthe*with_pip*parameter .. versionchanged:: 3.6Addedthe*prompt*parameter .. versionchanged:: 3.9Addedthe*upgrade_deps*parameter .. versionchanged:: 3.13Addedthe*scm_ignore_files*parameterThe following script shows how to extend :class:`EnvBuilder` by implementing a subclass which installs setuptools and pip into a created virtual environment:
importosimportos.pathfromsubprocessimportPopen, PIPEimportsysfromthreadingimportThreadfromurllib.parseimporturlparsefromurllib.requestimporturlretrieveimportvenvclassExtendedEnvBuilder(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) defpost_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_dirifnotself.nodist: self.install_setuptools(context) # Can't install pip without setuptoolsifnotself.nopipandnotself.nodist: self.install_pip(context) defreader(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.progresswhileTrue: s=stream.readline() ifnots: breakifprogressisnotNone: progress(s, context) else: ifnotself.verbose: sys.stderr.write('.') else: sys.stderr.write(s.decode('utf-8')) sys.stderr.flush() stream.close() definstall_script(self, context, name, url): _, _, path, _, _, _=urlparse(url) fn=os.path.split(path)[-1] binpath=context.bin_pathdistpath=os.path.join(binpath, fn) # Download script into the virtual environment's binaries folderurlretrieve(url, distpath) progress=self.progressifself.verbose: term='\n'else: term=''ifprogressisnotNone: progress('Installing %s ...%s'% (name, term), 'main') else: sys.stderr.write('Installing %s ...%s'% (name, term)) sys.stderr.flush() # Install in the virtual environmentargs= [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() ifprogressisnotNone: progress('done.', 'main') else: sys.stderr.write('done.\n') # Clean up - no longer neededos.unlink(distpath) definstall_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 downloadedpred=lambdao: o.startswith('setuptools-') ando.endswith('.tar.gz') files=filter(pred, os.listdir(context.bin_path)) forfinfiles: f=os.path.join(context.bin_path, f) os.unlink(f) definstall_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) defmain(args=None): importargparseparser=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.') ifos.name=='nt': use_symlinks=Falseelse: use_symlinks=Trueparser.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) ifoptions.upgradeandoptions.clear: raiseValueError('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) fordinoptions.dirs: builder.create(d) if__name__=='__main__': rc=1try: main() rc=0exceptExceptionase: print('Error: %s'%e, file=sys.stderr) sys.exit(rc)This script is also available for download online.
