Smallest Number in Infinite Set

class SmallestInfiniteSet:    import heapq    def __init__(self):        self.summary = list(range(1, 1001))        heapq.heapify(self.summary)        self.deleted = set()    def popSmallest(self) -> int:        A = heapq.heappop(self.summary)        self.deleted.add(A)        return A    def addBack(self, num: int) -> None:        if num in self.deleted:            self.deleted.remove(num)            heapq.heappush(self.summary, num)