python - segmentation fault, need to prevent this and reduce the run time of my program -

i solved problem had find sum of numbers digits made of 4, 5 , 6.. numbers have @ x fours, @ y fives , @ z sixes. passed of sample tests. but, cannot past other test cases keep getting segfault errors. also, think programs run time long. in reducing run time, optimizing solution , -reventing segfault appreciated. here code in python:

from itertools import permutations x , y, z = raw_input().split(' ') x = int(x) y = int(y) z = int(z) max = '' in range(z):     max += '6' b in range(y):     max += '5' c in range(x):     max += '4' perms = [''.join(p) p in permutations(max)] chances = [] def substring(string):     possible = []     x in range(len(string) + 1):         y in range(x, len(string) + 1):             possible.append(string[x:y])     return possible d in perms:     chances += list(set(substring(d))) chances = list(set(chances)) chances.remove('') sum = 0 nstr in chances:     sum += int(nstr) print sum  

it helpful know part of program consuming time. looking @ second half, after call permutations, see creating potentially huge lists (in chances , permutations. after building them convert set (to eliminate duplicates suppose) , again list. why not use single set instead, this:

chances = set() def substring(string):     x in range(len(string) + 1):         y in range(x, len(string) + 1):             chances.add(string[x:y]) d in perms:     substring(d) chances.remove('') sum = 0 nstr in chances:     sum += int(nstr) print sum  

i don't know if solve problems, should help.