import difflib

def solve(s1, s2):
    s = difflib.SequenceMatcher(None, s1, s2)
    block = s.get_matching_blocks()[0]
    if block.a == 0 and block.b == 0:
        return block.size / float(len(s1))

a = '354575368987943'
b = '354535368987000'
c = '354575368987000'
print solve(a, b)
print solve(a, c)