#!/usr/bin/env python

#

# relpath.py

# R.Barran 30/08/2004

# Retrieved from http://code.activestate.com/recipes/302594/

import os

import sys

def relpath(target, base=os.curdir):

    """

    Return a relative path to the target from either the current dir or an optional base dir.

    Base can be a directory specified either as absolute or relative to current dir.

    """

    if not os.path.exists(target):

        raise OSError, 'Target does not exist: '+target

    if not os.path.isdir(base):

        raise OSError, 'Base is not a directory or does not exist: '+base

    base_list = (os.path.abspath(base)).split(os.sep)

    target_list = (os.path.abspath(target)).split(os.sep)

    # On the windows platform the target may be on a completely different drive from the base.

    if os.name in ['nt','dos','os2'] and base_list[0] <> target_list[0]:

        raise OSError, 'Target is on a different drive to base. Target: '+target_list[0].upper()+', base: '+base_list[0].upper()

    # Starting from the filepath root, work out how much of the filepath is

    # shared by base and target.

    for i in range(min(len(base_list), len(target_list))):

        if base_list[i] <> target_list[i]: break

    else:

        # If we broke out of the loop, i is pointing to the first differing path elements.

        # If we didn't break out of the loop, i is pointing to identical path elements.

        # Increment i so that in all cases it points to the first differing path elements.

        i+=1

    rel_list = [os.pardir] * (len(base_list)-i) + target_list[i:]

    if (len(rel_list) == 0):

        return "."

    return os.path.join(*rel_list)

if __name__ == "__main__":

    print(relpath(sys.argv[1], sys.argv[2]))