gistfile1.py

from os import walk
from os.path import join
from sys import argv
from pprint import pprint

def collect_paths(path):
    file_paths = []
    for root, dirs, files in walk(path, topdown=False):
        for f in files:
            file_paths.append(join(root, f))
    return set(file_paths)

path_one = collect_paths(argv[1])
path_two = collect_paths(argv[2])

pprint(path_one.difference(path_two))