docs: def xpending_range(self, name, groupname, min, max, count,
                         consumername=None):
          """
          Returns information about pending messages, in a range.
          name: name of the stream.
          groupname: name of the consumer group.
          min: minimum stream ID.
          max: maximum stream ID.
          count: number of messages to return
          consumername: name of a consumer to filter by (optional).
          """
          pieces = [name, groupname]
          if min is not None or max is not None or count is not None:
              if min is None or max is None or count is None:
                  raise DataError("XPENDING must be provided with min, max "
                                  "and count parameters, or none of them. ")
              if not isinstance(count, (int, long)) or count < -1:
                  raise DataError("XPENDING count must be a integer >= -1")
              pieces.extend((min, max, str(count)))
          if consumername is not None:
              if min is None or max is None or count is None:
                  raise DataError("if XPENDING is provided with consumername,"
                                  " it must be provided with min, max and"
                                  " count parameters")
              pieces.append(consumername)
          return self.execute_command('XPENDING', *pieces, parse_detail=True)