"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, 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
"main()" function.

Cambiato nella versione 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/python*X.Y*/site-packages" (on Unix and macOS).  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.

Cambiato nella versione 3.5: Support for the "site-python" directory
has been removed.

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 (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 "true" (case-insensitive), the system-level prefixes will not be
searched for site-packages; otherwise they will.

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.

Nota:

  An executable line in a ".pth" file is run at every Python startup,
  regardless of whether a particular module is actually going to be
  used. Its impact should thus be kept to a minimum. The primary
  intended purpose of executable lines is to make the corresponding
  module(s) importable (load 3rd-party import hooks, adjust "PATH"
  etc). Any other initialization is supposed to be done upon a
  module's actual import, if and when it happens. Limiting a code
  chunk to a single line is a deliberate measure to discourage putting
  anything more complex here.

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.


"sitecustomize"
===============

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" or its subclass exception, and the exception's "name"
attribute equals to "'sitecustomize'", 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 other exception
causes a silent and perhaps mysterious failure of the process.


"usercustomize"
===============

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".  If this import fails
with an "ImportError" or its subclass exception, and the exception's
"name" attribute equals to "'usercustomize'", it is 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.


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.

Cambiato nella versione 3.4: Activation of rlcompleter and history was
made automatic.


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/python*X.Y*/site-packages" for UNIX and non-
   framework macOS builds, "~/Library/Python/*X.Y*/lib/python/site-
   packages" for macOS 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.

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 macOS non-framework builds,
   "~/Library/Python/*X.Y*" for macOS 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.

   Cambiato nella versione 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.

   Nuovo nella versione 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".

   Nuovo nella versione 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 "USER_BASE".  To determine if the user-specific
   site-packages was added to "sys.path" "ENABLE_USER_SITE" should be
   used.

   Nuovo nella versione 3.2.


Command Line Interface
======================

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:
"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.

Vedi anche:

  * **PEP 370** -- Per user site-packages directory

  * The initialization of the sys.path module search path -- The
    initialization of "sys.path".
