So yeah, just to put it all together, try this. From your two Ks, it either returns K+1 if it can or an empty string.
def k2k1(string1, string2): for c in string1: string2 = string2.replace(c,"",1) if len(string2) == 1: string1 += string2 else: string1 = "" return string1 Testing: print k2k1("abcdadd", "abceadd") gives: abcdadde -- http://mail.python.org/mailman/listinfo/python-list