pq_4.py

    def pull(self) -> Union[str, None]:
        """
        Return and remove the task with the highest priority.
        Since Python's heapq is implemented as a min heap, a
        smaller number mean the higher priority, i.e. priority 1
        has a higher priority that priority 2.

        Elements with same priority are pulled in the order of
        insertion.
        """
        if self.is_empty():
            return None
        return heapq.heappop(self.pqueue)[2]