python - Flask-PyMongo : how come "self._Collection__database"?

Question

在Flask-PyMongo中，他们使用self._Collection__database来表示这个Collection对象所属的数据库对象:

class Collection(collection.Collection):
    """Custom sub-class of :class:`pymongo.collection.Collection` which
    adds Flask-specific helper methods.
    """

    def __getattr__(self, name):
    attr = super(Collection, self).__getattr__(name)
    if isinstance(attr, collection.Collection):
        db = self._Collection__database
        return Collection(db, attr.name)
    return attr

为什么 self._Collection__database 不是 self.__database？

test <a>and <i>

Answer 1

Flask-PyMongo 并不是随意选择的名称。
名称是 name mangling 的结果:

Since there is a valid use-case for class-private members (namely to avoid name clashes of names with names defined by subclasses), there is limited support for such a mechanism, called name mangling. Any identifier of the form __spam (at least two leading underscores, at most one trailing underscore) is textually replaced with _classname__spam, where classname is the current class name with leading underscore(s) stripped.

在the parent-class definition ，该属性被定义为 self.__database 并且 Python“破坏”名称(到 self._ClassName__attributename)，这样任何子类都不会被自己的赋值覆盖self.__database 属性。