code: def get_assigned_value(self, name):
          
          message_type = type(self)
          try:
              field = message_type.field_by_name(name)
          except KeyError:
              raise AttributeError('Message %s has no field %s' % (
                  message_type.__name__, name))
          return self.__tags.get(field.number)
docs: Get the assigned value of an attribute.
  
          Get the underlying value of an attribute. If value has not
          been set, will not return the default for the field.
  
          Args:
            name: Name of attribute to get.
  
          Returns:
            Value of attribute, None if it has not been set.