Doc/library/site.rst

:mod:`site` --- Site-specific configuration hook
================================================

.. module:: site
   :synopsis: Module responsible for site-specific configuration.

**Source code:** :source:`Lib/site.py`

--------------

.. highlightlang:: none

**This module is automatically imported during initialization.** The automatic
import can be suppressed using the interpreter's :option:`-S` option.

.. index:: triple: module; search; path

Importing this module will append site-specific paths to the module search path
and add a few builtins.

.. index::
   pair: site-python; directory
   pair: site-packages; directory

It starts by constructing up to four directories from a head and a tail part.
For the head part, it uses ``sys.prefix`` and ``sys.exec_prefix``; empty heads
are skipped.  For the tail part, it uses the empty string and then
:file:`lib/site-packages` (on Windows) or
:file:`lib/python{X.Y}/site-packages` and then :file:`lib/site-python` (on
Unix and Macintosh).  For each of the distinct head-tail combinations, it sees
if it refers to an existing directory, and if so, adds it to ``sys.path`` and
also inspects the newly added path for configuration files.

A path configuration file is a file whose name has the form :file:`{name}.pth`
and exists in one of the four directories mentioned above; its contents are
additional items (one per line) to be added to ``sys.path``.  Non-existing items
are never added to ``sys.path``, and no check is made that the item refers to a
directory rather than a file.  No item is added to ``sys.path`` more than
once.  Blank lines and lines beginning with ``#`` are skipped.  Lines starting
with ``import`` (followed by space or tab) are executed.

.. versionchanged:: 2.6
   A space or tab is now required after the import keyword.

.. index::
   single: package
   triple: path; configuration; file

For example, suppose ``sys.prefix`` and ``sys.exec_prefix`` are set to
:file:`/usr/local`.  The Python X.Y library is then installed in
:file:`/usr/local/lib/python{X.Y}`.  Suppose this has
a subdirectory :file:`/usr/local/lib/python{X.Y}/site-packages` with three
subsubdirectories, :file:`foo`, :file:`bar` and :file:`spam`, and two path
configuration files, :file:`foo.pth` and :file:`bar.pth`.  Assume
:file:`foo.pth` contains the following::

   # foo package configuration

   foo
   bar
   bletch

and :file:`bar.pth` contains::

   # bar package configuration

   bar

Then the following version-specific directories are added to
``sys.path``, in this order::

   /usr/local/lib/pythonX.Y/site-packages/bar
   /usr/local/lib/pythonX.Y/site-packages/foo

Note that :file:`bletch` is omitted because it doesn't exist; the :file:`bar`
directory precedes the :file:`foo` directory because :file:`bar.pth` comes
alphabetically before :file:`foo.pth`; and :file:`spam` is omitted because it is
not mentioned in either path configuration file.

.. index:: module: sitecustomize

After these path manipulations, an attempt is made to import a module named
:mod:`sitecustomize`, which can perform arbitrary site-specific customizations.
It is typically created by a system administrator in the site-packages
directory.  If this import fails with an :exc:`ImportError` exception, it is
silently ignored.  If Python is started without output streams available, as
with :file:`pythonw.exe` on Windows (which is used by default to start IDLE),
attempted output from :mod:`sitecustomize` is ignored. Any exception other
than :exc:`ImportError` causes a silent and perhaps mysterious failure of the
process.

.. index:: module: usercustomize

After this, an attempt is made to import a module named :mod:`usercustomize`,
which can perform arbitrary user-specific customizations, if
:data:`ENABLE_USER_SITE` is true.  This file is intended to be created in the
user site-packages directory (see below), which is part of ``sys.path`` unless
disabled by :option:`-s`.  An :exc:`ImportError` will be silently ignored.

Note that for some non-Unix systems, ``sys.prefix`` and ``sys.exec_prefix`` are
empty, and the path manipulations are skipped; however the import of
:mod:`sitecustomize` and :mod:`usercustomize` is still attempted.


.. data:: PREFIXES

   A list of prefixes for site-packages directories.

   .. versionadded:: 2.6


.. data:: ENABLE_USER_SITE

   Flag showing the status of the user site-packages directory.  ``True`` means
   that it is enabled and was added to ``sys.path``.  ``False`` means that it
   was disabled by user request (with :option:`-s` or
   :envvar:`PYTHONNOUSERSITE`).  ``None`` means it was disabled for security
   reasons (mismatch between user or group id and effective id) or by an
   administrator.

   .. versionadded:: 2.6


.. data:: USER_SITE

   Path to the user site-packages for the running Python.  Can be ``None`` if
   :func:`getusersitepackages` hasn't been called yet.  Default value is
   :file:`~/.local/lib/python{X.Y}/site-packages` for UNIX and non-framework Mac
   OS X builds, :file:`~/Library/Python/{X.Y}/lib/python/site-packages` for Mac
   framework builds, and :file:`{%APPDATA%}\\Python\\Python{XY}\\site-packages`
   on Windows.  This directory is a site directory, which means that
   :file:`.pth` files in it will be processed.

   .. versionadded:: 2.6


.. data:: USER_BASE

   Path to the base directory for the user site-packages.  Can be ``None`` if
   :func:`getuserbase` hasn't been called yet.  Default value is
   :file:`~/.local` for UNIX and Mac OS X non-framework builds,
   :file:`~/Library/Python/{X.Y}` for Mac framework builds, and
   :file:`{%APPDATA%}\\Python` for Windows.  This value is used by Distutils to
   compute the installation directories for scripts, data files, Python modules,
   etc. for the :ref:`user installation scheme <inst-alt-install-user>`.  See
   also :envvar:`PYTHONUSERBASE`.

   .. versionadded:: 2.6


.. function:: addsitedir(sitedir, known_paths=None)

   Add a directory to sys.path and process its :file:`.pth` files.  Typically
   used in :mod:`sitecustomize` or :mod:`usercustomize` (see above).


.. function:: getsitepackages()

   Return a list containing all global site-packages directories (and possibly
   site-python).

   .. versionadded:: 2.7


.. function:: getuserbase()

   Return the path of the user base directory, :data:`USER_BASE`.  If it is not
   initialized yet, this function will also set it, respecting
   :envvar:`PYTHONUSERBASE`.

   .. versionadded:: 2.7


.. function:: getusersitepackages()

   Return the path of the user-specific site-packages directory,
   :data:`USER_SITE`.  If it is not initialized yet, this function will also set
   it, respecting :envvar:`PYTHONNOUSERSITE` and :data:`USER_BASE`.

   .. versionadded:: 2.7


The :mod:`site` module also provides a way to get the user directories from the
command line:

.. code-block:: sh

   $ python -m site --user-site
   /home/user/.local/lib/python2.7/site-packages

.. program:: site

If it is called without arguments, it will print the contents of
:data:`sys.path` on the standard output, followed by the value of
:data:`USER_BASE` and whether the directory exists, then the same thing for
:data:`USER_SITE`, and finally the value of :data:`ENABLE_USER_SITE`.

.. cmdoption:: --user-base

   Print the path to the user base directory.

.. cmdoption:: --user-site

   Print the path to the user site-packages directory.

If both options are given, user base and user site will be printed (always in
this order), separated by :data:`os.pathsep`.

If any option is given, the script will exit with one of these values: ``O`` if
the user site-packages directory is enabled, ``1`` if it was disabled by the
user, ``2`` if it is disabled for security reasons or by an administrator, and a
value greater than 2 if there is an error.

.. seealso::

   :pep:`370` -- Per user site-packages directory