cpython/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, unless :option:`-S` was used.  In that case, this module
can be safely imported with no automatic modifications to the module search path
or additions to the builtins.  To explicitly trigger the usual site-specific
additions, call the :func:`site.main` function.

.. versionchanged:: 3.3
   Importing the module used to trigger paths manipulation even when using
   :option:`-S`.

.. 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|version|/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.

If a file named "pyvenv.cfg" exists one directory above sys.executable,
sys.prefix and sys.exec_prefix are set to that directory and
it is also checked for site-packages and site-python (sys.base_prefix and
sys.base_exec_prefix will always be the "real" prefixes of the Python
installation). If "pyvenv.cfg" (a bootstrap configuration file) contains
the key "include-system-site-packages" set to anything other than "false"
(case-insensitive), the system-level prefixes will still also be
searched for site-packages; otherwise they won't.

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.

.. 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.

.. 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.


.. 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.


.. 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.


.. 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`.


.. function:: main()

   Adds all the standard site-specific directories to the module search
   path.  This function is called automatically when this module is imported,
   unless the :program:`python` interpreter was started with the :option:`-S`
   flag.

   .. versionchanged:: 3.3
      This function used to be called unconditionnally.


.. 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:: 3.2


.. 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:: 3.2


.. 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:: 3.2


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

.. code-block:: sh

   $ python3 -m site --user-site
   /home/user/.local/lib/python3.3/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