datastore.py 文件源码

def __setitem__(self, query_filter, value):
    """Add a new filter by setting it on all subqueries.

    If any of the setting operations raise an exception, the ones
    that succeeded are undone and the exception is propagated
    upward.

    Args:
      query_filter: a string of the form "property operand".
      value: the value that the given property is compared against.
    """
    saved_items = []
    for index, query in enumerate(self.__bound_queries):
      saved_items.append(query.get(query_filter, None))
      try:
        query[query_filter] = value
      except:
        for q, old_value in itertools.izip(self.__bound_queries[:index],
                                           saved_items):
          if old_value is not None:
            q[query_filter] = old_value
          else:
            del q[query_filter]
        raise