28.14. "site" — Site-specific configuration hook
************************************************

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

======================================================================

**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.

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/python*X.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.

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.

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

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/python*X.Y*".  Suppose this has a subdirectory
"/usr/local/lib/python*X.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.

site.PREFIXES

   A list of prefixes for site-packages directories.

   2.6 版新加入.

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.

   2.6 版新加入.

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/python*X.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\Python*XY*\site-packages" on Windows.  This
   directory is a site directory, which means that ".pth" files in it
   will be processed.

   2.6 版新加入.

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".

   2.6 版新加入.

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).

   2.7 版新加入.

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".

   2.7 版新加入.

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".

   2.7 版新加入.

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

   $ python -m site --user-site
   /home/user/.local/lib/python2.7/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:
"0" 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.

也參考: **PEP 370** – Per user site-packages directory
