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This only applies when os.name == 'posix'.
Running an un-installed build of Python with the -S
option causes the directory containing the standard
dynamically-built modules not to be placed on sys.path.
The build/lib.<platform>-<version>/ directory
containing those modules is added to sys.path by
site.py rather than getpath.c, even though those
modules are needed. This includes many modules on most
Unix systems:
array dbm math regex termios
audioop dl md5 resource _testcapi
binascii errno mmap rgbimg time
bsddb fcntl mpz rotor timing
cmath fpectl nis select _tkinter
_codecs gdbm operator sha 
unicodedata
cPickle grp parser _socket _weakref
crypt _hotshot pcre _ssl 
xreadlines
cStringIO _hotshot pwd strop zlib
_curses_panel linuxaudiodev pyexpat struct
_curses _locale readline syslog
Perhaps the best way to fix this is to add the
equivalent code to getpath.c. The relevant stanza in
site.py is headed by a comment saying "especially for
Guido".