code: def archive(cls):
      
      req = datastore.BeginTransactionRequest()
      resp = datastore.begin_transaction(req)
      tx = resp.transaction
      req = datastore.RunQueryRequest()
      req.read_options.transaction = tx
      q = req.query
      set_kind(q, kind='Todo')
      add_projection(q, '__key__')
      set_composite_filter(q.filter,
                           datastore.CompositeFilter.AND,
                           set_property_filter(
                               datastore.Filter(),
                               'done', datastore.PropertyFilter.EQUAL, True),
                           set_property_filter(
                               datastore.Filter(),
                               '__key__', datastore.PropertyFilter.HAS_ANCESTOR,
                               default_todo_list.key))
      resp = datastore.run_query(req)
      req = datastore.CommitRequest()
      req.transaction = tx
      for result in resp.batch.entity_results:
        req.mutations.add().delete.CopyFrom(result.entity.key)
      resp = datastore.commit(req)
      return ''
docs: Delete all Todo items that are done.