code: def generate(regex, Ns):
      "Return the strings matching regex whose length is in Ns."
      return sorted(regex_parse(regex)[0](Ns),
                    key=lambda s: (len(s), s)f generate(regex, Ns):
      "Return the strings matching regex whose length is in Ns."
      return sorted(regex_parse(regex)[0](Ns),
                    key=lambda s: (len(s), s))
docs: Return the strings matching regex whose length is in Ns.