1. Larry Hastings
  2. python-clinic


python-clinic / Doc / library / site.rst

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

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

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

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.

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.

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.

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


and :file:`bar.pth` contains:

# bar package configuration


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


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.

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.

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.

Readline configuration

On systems that support :mod:`readline`, this module will also import and configure the :mod:`rlcompleter` module, if Python is started in :ref:`interactive mode <tut-interactive>` and without the :option:`-S` option. The default behavior is enable tab-completion and to use :file:`~/.python_history` as the history save file. To disable it, override the :data:`sys.__interactivehook__` attribute in your :mod:`sitecustomize` or :mod:`usercustomize` module or your :envvar:`PYTHONSTARTUP` file.

Module contents

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

$ python3 -m site --user-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`.

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.