Common operations on Posix pathnames.
Instead of importing this module directly, import os and refer to
this module as os.path. The "os.path" name is an alias for this
module on Posix systems; on other systems (e.g. Windows),
os.path provides the same operations in a manner specific to that
platform, and is an alias to another module (e.g. ntpath).
Some of this can actually be useful on non-Posix systems too, e.g.
for manipulation of the pathname component of URLs.