code: def verify_utctz(offset):
      
      fmt_exc = ValueError("Invalid timezone offset format: %s" % offset)
      if len(offset) != 5:
          raise fmt_exc
      if offset[0] not in "+-":
          raise fmt_exc
      if offset[1] not in digits or\
         offset[2] not in digits or\
         offset[3] not in digits or\
         offset[4] not in digits:
          raise fmt_exc
      # END for each char
      return offset
docs: :raise ValueError: if offset is incorrect
      :return: offset