29.13. site — Site-specific configuration hook

Source code: Lib/site.py

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

Importing this module will append site-specific paths to the module search path and add a few builtins, unless -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 site.main() function.

Changed in version 3.3: Importing the module used to trigger paths manipulation even when using -S.

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 lib/site-packages (on Windows) or lib/pythonX.Y/site-packages and then 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.

Deprecated since version 3.4: Support for the “site-python” directory will be removed in 3.5.

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 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 /usr/local. The Python X.Y library is then installed in /usr/local/lib/pythonX.Y. Suppose this has a subdirectory /usr/local/lib/pythonX.Y/site-packages with three subsubdirectories, foo, bar and spam, and two path configuration files, foo.pth and bar.pth. Assume foo.pth contains the following:

# foo package configuration

foo
bar
bletch

and 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 bletch is omitted because it doesn’t exist; the bar directory precedes the foo directory because bar.pth comes alphabetically before foo.pth; and 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 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 ImportError exception, it is silently ignored. If Python is started without output streams available, as with pythonw.exe on Windows (which is used by default to start IDLE), attempted output from sitecustomize is ignored. Any exception other than ImportError causes a silent and perhaps mysterious failure of the process.

After this, an attempt is made to import a module named usercustomize, which can perform arbitrary user-specific customizations, if 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 -s. An 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 sitecustomize and usercustomize is still attempted.

29.13.1. Readline configuration

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

Changed in version 3.4: Activation of rlcompleter and history was made automatic.

29.13.2. Module contents

site.PREFIXES

A list of prefixes for site-packages directories.

site.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 -s or PYTHONNOUSERSITE). None means it was disabled for security reasons (mismatch between user or group id and effective id) or by an administrator.

site.USER_SITE

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

site.USER_BASE

Path to the base directory for the user site-packages. Can be None if getuserbase() hasn’t been called yet. Default value is ~/.local for UNIX and Mac OS X non-framework builds, ~/Library/Python/X.Y for Mac framework builds, and %APPDATA%\Python for Windows. This value is used by Distutils to compute the installation directories for scripts, data files, Python modules, etc. for the user installation scheme. See also PYTHONUSERBASE.

site.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 Python interpreter was started with the -S flag.

Changed in version 3.3: This function used to be called unconditionally.

site.addsitedir(sitedir, known_paths=None)

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

site.getsitepackages()

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

New in version 3.2.

site.getuserbase()

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

New in version 3.2.

site.getusersitepackages()

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

New in version 3.2.

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

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

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

--user-base

Print the path to the user base directory.

--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 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.

See also

PEP 370 – Per user site-packages directory