重写自定义类的枚举

问：

我有一个自定义类，它本质上是一个列表，但负索引是有效的索引，而不是引用列表后面的元素。

from collections.abc import Sequence


class MultiFloorPlan(Sequence):
    def __init__(self):
        super().__init__()
        self._floors = []
        self._subfloors = []

    def __eq__(self, other):
        if not isinstance(other, MultiFloorPlan):
            return NotImplemented
        return self._subfloors == other._subfloors and self._floors == other._floors

    def _reindex(self, floor):
        if floor >= 0:
            return self._floors, floor
        return self._subfloors, -floor - 1

    def __len__(self):
        return len(self._subfloors) + len(self._floors)

    def __getitem__(self, floor):
        floor_list, floor = self._reindex(floor)
        return floor_list[floor]

    def __delitem__(self, floor):
        floor_list, floor = self._reindex(floor)
        del floor_list[floor]

    def __iter__(self):
        for plan in self._subfloors:
            yield plan
        for plan in self._floors:
            yield plan

    def __reversed__(self):
        for plan in reversed(self._floors):
            yield plan
        for plan in reversed(self._subfloors):
            yield plan

    def __contains__(self, value):
        return value in self._subfloors or value in self._floors

    def append(self, subfloor=False):
        if subfloor:
            return self._subfloors.append(None)  # For this example we append a dummy None
        return self._floors.append(None)         # value instead of an actual Plan instance

是否有可能让内置的返回地板索引，而不是将值转移到非负整数？例：enumerate

mfp = MultiFloorPlan()
for _ in range(5):
    mfp.append(subfloor=False)
    mfp.append(subfloor=True)

for floor, _ in enumerate(mfp):
    print(floor)
# This prints 0 1 2 3 4 5 6 7 8 9, but I'd like it to print -5 -4 -3 -2 -1 0 1 2 3 4