Python - how to find all intersections of two strings?

Question

How to find all intersections (also called the longest common substrings) of two strings and their positions in both strings?

For example, if S1=\"never\"

Answer 1

Here's what I could come up with:

import itertools

def longest_common_substring(s1, s2):
   set1 = set(s1[begin:end] for (begin, end) in
              itertools.combinations(range(len(s1)+1), 2))
   set2 = set(s2[begin:end] for (begin, end) in
              itertools.combinations(range(len(s2)+1), 2))
   common = set1.intersection(set2)
   maximal = [com for com in common
              if sum((s.find(com) for s in common)) == -1 * (len(common)-1)]
   return [(s, s1.index(s), s2.index(s)) for s in maximal]

Checking some values:

>>> longest_common_substring('address', 'oddness')
[('dd', 1, 1), ('ess', 4, 4)]
>>> longest_common_substring('never', 'forever')
[('ever', 1, 3)]
>>> longest_common_substring('call', 'wall')
[('all', 1, 1)]
>>> longest_common_substring('abcd1234', '1234abcd')
[('abcd', 0, 4), ('1234', 4, 0)]