Improve documentation for PEP 370 support in site module (#8617).

site.USER_BASE and site.USER_SITE are now fully documented.  PEP 370 is
outdated with respects to the Mac framework situation, but the code in
sysconfig and the example in the 3.2 What’s New document helped me find
the right values to document for Mac OS X.

The command-line interface of the site module, partly documented in the
3.2 What’s New, is fully described in the module docs.

The purpose of the usercustomize module is explained in the site docs,
with a gentle introduction in the tutorial (right after the section that
talks about PYTHONSTARTUP; a comment mentions it should be moved from
the tutorial to another file, but that will be another bug).

Various markup and wording improvements were made along the way in the
site module docs.  Duplicate and incomplete declarations of environment
variables have also been removed (the original bug report was actually
about these entries :).  The site module docs are still a bit messy;
I’ll see about improving them for #11553.

All these sections are copiously interlinked and findable from the doc
indexes.

1 files changed, 86 insertions, 36 deletions

diff --git a/Doc/library/site.rst b/Doc/library/site.rst
index b77f3cf..adab800 100644
--- a/Doc/library/site.rst
+++ b/Doc/library/site.rst
@@ -2,18 +2,21 @@
 ================================================
 
 .. module:: site
-   :synopsis: A standard way to reference site-specific modules.
+   :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.
+Importing this module will append site-specific paths to the module search path
+and add a few builtins.
 
 .. index::
    pair: site-python; directory
@@ -28,11 +31,11 @@ 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:`package.pth`
+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``, but no check is made that the item refers to a
-directory (rather than a file).  No item is added to ``sys.path`` more than
+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.
 
@@ -42,8 +45,7 @@ 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}` (where only the first three characters of
-``sys.version`` are used to form the installation path name).  Suppose this has
+: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
@@ -76,74 +78,122 @@ 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.
-If this import fails with an :exc:`ImportError` exception, it is silently
-ignored.
+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: sitecustomize
+.. 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` is still attempted.
+:mod:`sitecustomize` and :mod:`usercustomize` is still attempted.
 
 
 .. data:: PREFIXES
 
-   A list of prefixes for site package directories
+   A list of prefixes for site-packages directories.
 
 
 .. data:: ENABLE_USER_SITE
 
-   Flag showing the status of the user site directory. True means the
-   user site directory is enabled and added to sys.path. When the flag
-   is None the user site directory is disabled for security reasons.
+   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 directory for the current Python version or None
+   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 user site directories
+   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.  See also :envvar:`PYTHONUSERBASE`.
 
 
-.. envvar:: PYTHONNOUSERSITE
+.. function:: addsitedir(sitedir, known_paths=None)
 
+   Add a directory to sys.path and process its :file:`.pth` files.
 
-.. envvar:: PYTHONUSERBASE
 
+.. function:: getsitepackages()
 
-.. function:: addsitedir(sitedir, known_paths=None)
+   Return a list containing all global site-packages directories (and possibly
+   site-python).
 
-   Adds a directory to sys.path and processes its pth files.
+   .. versionadded:: 3.2
 
-.. function:: getsitepackages()
 
-   Returns a list containing all global site-packages directories
-   (and possibly site-python).
+.. 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:: getuserbase()
 
-   Returns the "user base" directory path.
+.. function:: getusersitepackages()
 
-   The "user base" directory can be used to store data. If the global
-   variable ``USER_BASE`` is not initialized yet, this function will also set
-   it.
+   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
 
-.. function:: getusersitepackages()
 
-   Returns the user-specific site-packages directory path.
+The :mod:`site` module also provides a way to get the user directories from the
+command line:
 
-   If the global variable ``USER_SITE`` is not initialized yet, this
-   function will also set it.
+.. code-block:: sh
 
-   .. versionadded:: 3.2
+   $ 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.
 
-.. XXX Update documentation
-.. XXX document python -m site --user-base --user-site
+.. seealso::
 
+   :pep:`370` -- Per user site-packages directory