A better answer would be to use os.path.relpath:
http://docs.python.org/2/library/os.path.html#os.path.relpathhttp://docs.python.org/3/library/os.path.html#os.path.relpath
>>> import os
>>> full_path = '/book/html/wa/foo/bar/'
>>> printrelative_path = '/book/html'
>>> print(os.path.relpath(full_path, '/book/html'relative_path))
'wa/foo/bar'