def first_diff(a, b):
    
    i = -1
    for i in xrange(0, len(a)):
        if a[i] != b[1]:
            return i
        if i == 255: return i
    return i + 1
Returns the position of the first differing character in the strings
dataset/ETHPy150Open tallstreet/Whoosh-AppEngine/src/whoosh/util.py/first_diff