difflib SequenceMatcher - most common substring in list of strings

# -*- coding: utf-8 -*-
from difflib import SequenceMatcher

def f1(string_list):
	d = {}
	for s in string_list:
		d[s] = score(s, string_list)
	return d

def score(string, string_list):
	x = [i for i in [SequenceMatcher(None, string, s).ratio() for s in string_list if not s == string] if i > 0]
	return max(x)+min(x)-(sum(x)/len(x))

string_list = ['abcde', 'abcde fg', 'abc', 'fg', 'abcfg', ' ']
r = f1(string_list)