code: def unpack(self, buff, offset=0):
          
          begin = offset
          for name, value in list(self.get_class_attributes())[:-1]:
              size = self._unpack_attribute(name, value, buff, begin)
              begin += size
          self._unpack_attribute('oxm_match_fields', type(self).oxm_match_fields,
                                 buff[:offset+self.length], begin)
docs: Discard padding bytes using the unpacked length attribute.