code: def add_converter(self, klass, conv, score=0):
          
          if isinstance(klass, str):
              klass = import_obj(klass)
          item = score, klass, conv
          self.converters.append(item)
          self.converters.sort(key=lambda x: x[0])
          return self
docs: Add converter
          :param klass: class or str
          :param conv: callable
          :param score:
          :return: