code: def _parse_filter_string(filter_string):
      
      assert "=" in filter_string, "filter string requires an '=', got {0}".format(filter_string)
      split_values = filter_string.split('=')
      assert len(split_values) == 2, "more than one equals found in filter string {0}!".format(filter_string)
      return split_values
docs: parse a filter string into a key-value pair