cpython/Lib/site.py

"""Append module search paths for third-party packages to sys.path.

****************************************************************
* This module is automatically imported during initialization. *
****************************************************************

In earlier versions of Python (up to 1.5a3), scripts or modules that
needed to use site-specific modules would place ``import site''
somewhere near the top of their code.  Because of the automatic
import, this is no longer necessary (but code that does it still
works).

This will append site-specific paths to to the module search path.  It
starts with sys.prefix and sys.exec_prefix (if different) and appends
lib/python<version>/packages.  The resulting directory, if it exists,
is added to sys.path, and also inspected for path configuration files.

A path configuration file is a file whose name has the form
<package>.pth; its contents are additional directories (one per line)
to be added to sys.path.  Non-existing directories (or
non-directories) are never added to sys.path; no directory is added to
sys.path more than once.  Blank lines and lines beginning with
\code{#} are skipped.

For example, suppose sys.prefix and sys.exec_prefix are set to
/usr/local and there is a directory /usr/local/python1.5/packages with
three subdirectories, 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 directories are added to sys.path, in this order:

  /usr/local/lib/python1.5/packages/bar
  /usr/local/lib/python1.5/packages/foo

Note that bletch is omitted because it doesn't exist; bar precedes foo
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 additional
site-specific customizations.  If this import fails with an
ImportError exception, it is silently ignored.

Note that for some non-Unix systems, sys.prefix and sys.exec_prefix
are empty, and then the path manipulations are skipped; however the
import of sitecustomize is still attempted.

"""

import sys, os

def addsitedir(sitedir):
    if sitedir not in sys.path:
	sys.path.append(sitedir)	# Add path component
    try:
	names = os.listdir(sitedir)
    except os.error:
	return
    names = map(os.path.normcase, names)
    names.sort()
    for name in names:
	if name[-4:] == ".pth":
	    addpackage(sitedir, name)

def addpackage(sitedir, name):
    fullname = os.path.join(sitedir, name)
    try:
	f = open(fullname)
    except IOError:
	return
    while 1:
	dir = f.readline()
	if not dir:
	    break
	if dir[0] == '#':
	    continue
	if dir[-1] == '\n':
	    dir = dir[:-1]
	dir = os.path.join(sitedir, dir)
	if dir not in sys.path and os.path.exists(dir):
	    sys.path.append(dir)

prefixes = [sys.prefix]
if sys.exec_prefix != sys.prefix:
    prefixes.append(sys.exec_prefix)
for prefix in prefixes:
    if prefix:
	if sys.platform[:3] in ('win', 'mac'):
	    sitedir = prefix
	else:
	    sitedir = os.path.join(prefix,
				   "lib",
				   "python" + sys.version[:3],
				   "packages")
	if os.path.isdir(sitedir):
	    addsitedir(sitedir)

try:
    import sitecustomize		# Run arbitrary site specific code
except ImportError:
    pass				# No site customization module

def _test():
    print "sys.path = ["
    for dir in sys.path:
	print "    %s," % `dir`
    print "]"

if __name__ == '__main__':
    _test()