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392 lines
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ReStructuredText
392 lines
17 KiB
ReStructuredText
:mod:`venv` --- Creation of virtual environments
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================================================
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.. module:: venv
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:synopsis: Creation of virtual environments.
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.. moduleauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk>
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.. sectionauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk>
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.. index:: pair: Environments; virtual
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.. versionadded:: 3.3
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**Source code:** :source:`Lib/venv.py`
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--------------
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The :mod:`venv` module provides support for creating lightweight "virtual
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environments" with their own site directories, optionally isolated from system
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site directories. Each virtual environment has its own Python binary (allowing
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creation of environments with various Python versions) and can have its own
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independent set of installed Python packages in its site directories.
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Creating virtual environments
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-----------------------------
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.. include:: /using/venv-create.inc
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.. _venv-def:
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.. note:: A virtual environment (also called a ``venv``) is a Python
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environment such that the Python interpreter, libraries and scripts
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installed into it are isolated from those installed in other virtual
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environments, and (by default) any libraries installed in a "system" Python,
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i.e. one which is installed as part of your operating system.
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A venv is a directory tree which contains Python executable files and
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other files which indicate that it is a venv.
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Common installation tools such as ``Distribute`` and ``pip`` work as
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expected with venvs - i.e. when a venv is active, they install Python
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packages into the venv without needing to be told to do so explicitly.
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Of course, you need to install them into the venv first: this could be
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done by running ``distribute_setup.py`` with the venv activated,
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followed by running ``easy_install pip``. Alternatively, you could download
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the source tarballs and run ``python setup.py install`` after unpacking,
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with the venv activated.
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When a venv is active (i.e. the venv's Python interpreter is running), the
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attributes :attr:`sys.prefix` and :attr:`sys.exec_prefix` point to the base
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directory of the venv, whereas :attr:`sys.base_prefix` and
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:attr:`sys.base_exec_prefix` point to the non-venv Python installation
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which was used to create the venv. If a venv is not active, then
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:attr:`sys.prefix` is the same as :attr:`sys.base_prefix` and
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:attr:`sys.exec_prefix` is the same as :attr:`sys.base_exec_prefix` (they
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all point to a non-venv Python installation).
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API
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---
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.. highlight:: python
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The high-level method described above makes use of a simple API which provides
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mechanisms for third-party virtual environment creators to customize environment
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creation according to their needs, the :class:`EnvBuilder` class.
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.. class:: EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False)
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The :class:`EnvBuilder` class accepts the following keyword arguments on
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instantiation:
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* ``system_site_packages`` -- a Boolean value indicating that the system Python
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site-packages should be available to the environment (defaults to ``False``).
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* ``clear`` -- a Boolean value which, if True, will delete the contents of
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any existing target directory, before creating the environment.
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* ``symlinks`` -- a Boolean value indicating whether to attempt to symlink the
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Python binary (and any necessary DLLs or other binaries,
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e.g. ``pythonw.exe``), rather than copying. Defaults to ``True`` on Linux and
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Unix systems, but ``False`` on Windows.
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* ``upgrade`` -- a Boolean value which, if True, will upgrade an existing
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environment with the running Python - for use when that Python has been
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upgraded in-place (defaults to ``False``).
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Creators of third-party virtual environment tools will be free to use the
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provided ``EnvBuilder`` class as a base class.
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The returned env-builder is an object which has a method, ``create``:
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.. method:: create(env_dir)
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This method takes as required argument the path (absolute or relative to
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the current directory) of the target directory which is to contain the
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virtual environment. The ``create`` method will either create the
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environment in the specified directory, or raise an appropriate
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exception.
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The ``create`` method of the ``EnvBuilder`` class illustrates the hooks
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available for subclass customization::
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def create(self, env_dir):
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"""
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Create a virtualized Python environment in a directory.
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env_dir is the target directory to create an environment in.
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"""
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env_dir = os.path.abspath(env_dir)
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context = self.create_directories(env_dir)
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self.create_configuration(context)
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self.setup_python(context)
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self.setup_scripts(context)
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self.post_setup(context)
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Each of the methods :meth:`create_directories`,
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:meth:`create_configuration`, :meth:`setup_python`,
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:meth:`setup_scripts` and :meth:`post_setup` can be overridden.
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.. method:: create_directories(env_dir)
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Creates the environment directory and all necessary directories, and
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returns a context object. This is just a holder for attributes (such as
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paths), for use by the other methods.
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.. method:: create_configuration(context)
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Creates the ``pyvenv.cfg`` configuration file in the environment.
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.. method:: setup_python(context)
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Creates a copy of the Python executable (and, under Windows, DLLs) in
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the environment.
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.. method:: setup_scripts(context)
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Installs activation scripts appropriate to the platform into the virtual
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environment.
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.. method:: post_setup(context)
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A placeholder method which can be overridden in third party
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implementations to pre-install packages in the virtual environment or
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perform other post-creation steps.
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In addition, :class:`EnvBuilder` provides this utility method that can be
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called from :meth:`setup_scripts` or :meth:`post_setup` in subclasses to
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assist in installing custom scripts into the virtual environment.
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.. method:: install_scripts(context, path)
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*path* is the path to a directory that should contain subdirectories
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"common", "posix", "nt", each containing scripts destined for the bin
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directory in the environment. The contents of "common" and the
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directory corresponding to :data:`os.name` are copied after some text
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replacement of placeholders:
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* ``__VENV_DIR__`` is replaced with the absolute path of the environment
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directory.
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* ``__VENV_NAME__`` is replaced with the environment name (final path
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segment of environment directory).
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* ``__VENV_BIN_NAME__`` is replaced with the name of the bin directory
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(either ``bin`` or ``Scripts``).
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* ``__VENV_PYTHON__`` is replaced with the absolute path of the
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environment's executable.
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There is also a module-level convenience function:
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.. function:: create(env_dir, system_site_packages=False, clear=False, symlinks=False)
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Create an :class:`EnvBuilder` with the given keyword arguments, and call its
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:meth:`~EnvBuilder.create` method with the *env_dir* argument.
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An example of extending ``EnvBuilder``
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--------------------------------------
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The following script shows how to extend :class:`EnvBuilder` by implementing a
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subclass which installs Distribute and pip into a created venv::
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import os
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import os.path
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from subprocess import Popen, PIPE
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import sys
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from threading import Thread
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from urllib.parse import urlparse
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from urllib.request import urlretrieve
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import venv
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class DistributeEnvBuilder(venv.EnvBuilder):
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"""
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This builder installs Distribute and pip so that you can pip or
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easy_install other packages into the created environment.
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:param nodist: If True, Distribute is not installed into the created
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environment.
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:param nopip: If True, pip is not installed into the created
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environment.
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:param progress: If Distribute or pip are installed, the progress of the
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installation can be monitored by passing a progress
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callable. If specified, it is called with two
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arguments: a string indicating some progress, and a
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context indicating where the string is coming from.
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The context argument can have one of three values:
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'main', indicating that it is called from virtualize()
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itself, and 'stdout' and 'stderr', which are obtained
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by reading lines from the output streams of a subprocess
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which is used to install the app.
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If a callable is not specified, default progress
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information is output to sys.stderr.
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"""
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def __init__(self, *args, **kwargs):
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self.nodist = kwargs.pop('nodist', False)
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self.nopip = kwargs.pop('nopip', False)
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self.progress = kwargs.pop('progress', None)
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self.verbose = kwargs.pop('verbose', False)
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super().__init__(*args, **kwargs)
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def post_setup(self, context):
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"""
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Set up any packages which need to be pre-installed into the
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environment being created.
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:param context: The information for the environment creation request
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being processed.
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"""
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if not self.nodist:
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self.install_distribute(context)
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if not self.nopip:
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self.install_pip(context)
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def reader(self, stream, context):
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"""
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Read lines from a subprocess' output stream and either pass to a progress
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callable (if specified) or write progress information to sys.stderr.
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"""
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progress = self.progress
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while True:
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s = stream.readline()
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if not s:
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break
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if progress is not None:
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progress(s, context)
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else:
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if not self.verbose:
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sys.stderr.write('.')
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else:
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sys.stderr.write(s.decode('utf-8'))
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sys.stderr.flush()
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def install_script(self, context, name, url):
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_, _, path, _, _, _ = urlparse(url)
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fn = os.path.split(path)[-1]
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binpath = context.bin_path
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distpath = os.path.join(binpath, fn)
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# Download script into the env's binaries folder
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urlretrieve(url, distpath)
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progress = self.progress
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if progress is not None:
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progress('Installing %s' %name, 'main')
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else:
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sys.stderr.write('Installing %s ' % name)
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sys.stderr.flush()
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# Install in the env
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args = [context.env_exe, fn]
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p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
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t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
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t1.start()
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t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
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t2.start()
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p.wait()
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t1.join()
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t2.join()
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if progress is not None:
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progress('done.', 'main')
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else:
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sys.stderr.write('done.\n')
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# Clean up - no longer needed
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os.unlink(distpath)
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def install_distribute(self, context):
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"""
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Install Distribute in the environment.
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:param context: The information for the environment creation request
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being processed.
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"""
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url = 'http://python-distribute.org/distribute_setup.py'
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self.install_script(context, 'distribute', url)
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# clear up the distribute archive which gets downloaded
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pred = lambda o: o.startswith('distribute-') and o.endswith('.tar.gz')
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files = filter(pred, os.listdir(context.bin_path))
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for f in files:
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f = os.path.join(context.bin_path, f)
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os.unlink(f)
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def install_pip(self, context):
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"""
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Install pip in the environment.
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:param context: The information for the environment creation request
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being processed.
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"""
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url = 'https://raw.github.com/pypa/pip/master/contrib/get-pip.py'
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self.install_script(context, 'pip', url)
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def main(args=None):
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compatible = True
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if sys.version_info < (3, 3):
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compatible = False
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elif not hasattr(sys, 'base_prefix'):
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compatible = False
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if not compatible:
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raise ValueError('This script is only for use with '
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'Python 3.3 or later')
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else:
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import argparse
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parser = argparse.ArgumentParser(prog=__name__,
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description='Creates virtual Python '
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'environments in one or '
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'more target '
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'directories.')
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parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
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help='A directory to create the environment in.')
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parser.add_argument('--no-distribute', default=False,
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action='store_true', dest='nodist',
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help="Don't install Distribute in the virtual "
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"environment.")
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parser.add_argument('--no-pip', default=False,
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action='store_true', dest='nopip',
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help="Don't install pip in the virtual "
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"environment.")
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parser.add_argument('--system-site-packages', default=False,
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action='store_true', dest='system_site',
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help='Give the virtual environment access to the '
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'system site-packages dir.')
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if os.name == 'nt':
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use_symlinks = False
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else:
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use_symlinks = True
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parser.add_argument('--symlinks', default=use_symlinks,
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action='store_true', dest='symlinks',
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help='Try to use symlinks rather than copies, '
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'when symlinks are not the default for '
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'the platform.')
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parser.add_argument('--clear', default=False, action='store_true',
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dest='clear', help='Delete the contents of the '
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'environment directory if it '
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'already exists, before '
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'environment creation.')
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parser.add_argument('--upgrade', default=False, action='store_true',
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dest='upgrade', help='Upgrade the environment '
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'directory to use this version '
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'of Python, assuming Python '
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'has been upgraded in-place.')
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parser.add_argument('--verbose', default=False, action='store_true',
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dest='verbose', help='Display the output '
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'from the scripts which '
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'install Distribute and pip.')
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options = parser.parse_args(args)
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if options.upgrade and options.clear:
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raise ValueError('you cannot supply --upgrade and --clear together.')
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builder = DistributeEnvBuilder(system_site_packages=options.system_site,
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clear=options.clear,
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symlinks=options.symlinks,
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upgrade=options.upgrade,
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nodist=options.nodist,
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nopip=options.nopip,
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verbose=options.verbose)
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for d in options.dirs:
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builder.create(d)
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if __name__ == '__main__':
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rc = 1
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try:
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main()
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rc = 0
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except Exception as e:
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print('Error: %s' % e, file=sys.stderr)
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sys.exit(rc)
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This script is also available for download `online
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<https://gist.github.com/4673395>`_.
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