code: def _filter_result(result, filter_functions=None):
          
          if filter_functions is not None:
              for filter_func in filter_functions:
                  result = filter(filter_func, result)
          return result
docs: Filter result with given filter functions.
  
          :param result: an iterable object
          :param filter_functions: some filter functions
          :return: a filter object (filtered result)