code: def add_filter(self, filter):
          
          if not isinstance(filter, AbstractFilter):
              err = 'Filters must be of type {}'.format(AbstractFilter)
              raise InvalidFilter(err)
  
          if filter not in self.filters:
              self.filters.append(filter)
          return self
docs: Add filter to property
          :param filter: object, extending from AbstractFilter
          :return: None