How to calculate relative path between 2 directory path?

I have 2 directory:

subdir1 = live/events/livepkgr/events/_definst_/
subdir2 = live/streams/livepkgr/streams/_definst_/

result must be:

diff_subdir = ../../../开发者_运维问答../streams/livepkgr/streams/_definst_/

http://docs.python.org/library/os.path.html

os.path.relpath(path[, start]) Return a relative filepath to path either from the current directory or from an optional start point.

start defaults to os.curdir.

Availability: Windows, Unix.

New in version 2.6.

>>> subdir1 = "live/events/livepkgr/events/_definst_/"
>>> subdir2 = "live/streams/livepkgr/streams/_definst_/"
>>> import os
>>> os.path.relpath(subdir2, subdir1)
'../../../../streams/livepkgr/streams/_definst_'
>>>