docs: def _GetFormatter(self, format_str):
          """
      The user's formatters are consulted first, then the default formatters.
      """
          formatter, args, func_type = self.formatters.LookupWithType(format_str)
          if formatter:
              return formatter, args, func_type
          else:
              raise BadFormatter('%r is not a valid formatter' % format_str)