<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def count(self):
        "The number of items, pruned or otherwise, contained by this branch."
        if getattr(self, '_count', None) is None:
            self._count = getattr(self.node, 'count', 0)
        return self._count