def suffixPrefixMatch(str1, str2, min_overlap):
    ''' Returns length of longest suffix of str1 that is prefix of
        str2, as long as that suffix is at least as long as min_overlap. '''
    if len(str2) < min_overlap: return 0
    str2_prefix = str2[:min_overlap]
    str1_pos = -1
    while True:
        str1_pos = str1.find(str2_prefix, str1_pos + 1)
        if str1_pos == -1: return 0
        str1_suffix = str1[str1_pos:]
        if str2.startswith(str1_suffix): return len(str1_suffix)

# overlap is 'more'
suffixPrefixMatch('a little more', 'more than kin', min_overlap=3)

# len('more') < 5 so overlap won't be found
suffixPrefixMatch('a little more', 'more than kin', min_overlap=5)