First find a common path, afterwards split on os.sep. Handle the special case if the common path is actually root. Done. (If your code does not have to run on Windows that is…)

Check out the Gist.

import os

path1 = os.path.abspath('/home/winlu/gitrepos/commonmagic/')
path2 = os.path.abspath('/home/winlu/')
path3 = os.path.abspath('/home/winlu/youtubefiles/')
path4 = os.path.abspath('/var/log/')
path5 = os.path.abspath('/')

distance_1_2 = 2
distance_1_3 = 3
distance_2_3 = 1
distance_1_4 = 6
distance_1_5 = 4


def _sub_dir_count(path):
    return len(path.split(os.sep))

#wont work on windows, or some cases (1_5)
def calc_dist(path1,path2):
    prefix = os.path.abspath(os.path.commonprefix([path1,path2]))
    if(prefix==os.sep):
        prefix=''
    dist_a = _sub_dir_count(path1) - _sub_dir_count(prefix)
    dist_b = _sub_dir_count(path2) - _sub_dir_count(prefix)
    return dist_a + dist_b

#provided by saimn
def calc_dist2(p1, p2):
    path = os.path.relpath(p1, p2)
    return path.count(os.sep) + 1
    # or: len(path.split(os.sep))

assert (calc_dist(path1,path2) == distance_1_2)
assert (calc_dist(path1,path3) == distance_1_3)
assert (calc_dist(path2,path3) == distance_2_3)
assert (calc_dist(path1,path4) == distance_1_4)
#assert (calc_dist(path1,path5) == distance_1_5)

assert (calc_dist2(path1,path2) == distance_1_2)
assert (calc_dist2(path1,path3) == distance_1_3)
assert (calc_dist2(path2,path3) == distance_2_3)
assert (calc_dist2(path1,path4) == distance_1_4)
assert (calc_dist2(path1,path5) == distance_1_5)

This is just a quick hack, and will fail in some cases.

Use at own Risk.

- winlu