weakref.py 文件源码

def itervaluerefs(self):
        """Return an iterator that yields the weak references to the values.

        The references are not guaranteed to be 'live' at the time
        they are used, so the result of calling the references needs
        to be checked before being used.  This can be used to avoid
        creating references that will cause the garbage collector to
        keep the values around longer than needed.

        """
        if self._pending_removals:
            self._commit_removals()
        with _IterationGuard(self):
            yield from self.data.values()