code: def pack_tag(field_number, wire_type):
      
      if not 0 <= wire_type <= _WIRETYPE_MAX:
          raise errors.EncodeError('Unknown wire type: %d' % wire_type)
      return (field_number << TAG_TYPE_BITS) | wire_type
docs: Returns an unsigned 32-bit integer that encodes the field number and
      wire type information in standard protocol message wire format.
  
      Args:
        field_number: Expected to be an integer in the range [1, 1 << 29)
        wire_type: One of the WIRETYPE_* constants.