Python: dict supporting lazy sorting, Previous/Next item

myDict.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# (c) 2018 Florian Lagg <github@florian.lagg.at>
# Under Terms of GPL v3

class MyDict(dict):
    def __init__(self, *args, **kwargs):
        self._sortedList = None
        super(MyDict, self).__init__(*args, **kwargs)

    def __setitem__(self, key, value):
        self._sortedList = None
        return super(MyDict, self).__setitem__(key, value)
    def __delitem__(self, key):
        self._sortedList = None
        return super(MyDict, self).__delitem__(key)
    def pop(self, key):
        self._sortedList = None
        return super(MyDict, self).pop(key)

    @property
    def Sorted(self):
        if self._sortedList is None:
            self._sortedList = sorted(self)
        return self._sortedList

    def GetPrevKey(self, key):
        idx = self.Sorted.index(key)
        if idx == 0:
            return None
        else:
            return self.Sorted[idx-1]

    def GetNextKey(self, key):
        idx = self.Sorted.index(key)
        if idx+1 == len(self.Sorted):
            return None
        else:
            return self.Sorted[idx + 1]

    def _getKeyOrNone(self, key):
        if key is None:
            return None
        return self[key]

    def GetPrev(self, key):
        return self._getKeyOrNone(self.GetPrevKey(key))

    def GetNext(self, key):
        return self._getKeyOrNone(self.GetNextKey(key))

Works for me, but probably not every case. Feel free to comment.
Will be used here: https://github.com/LaggAt/DimensionTabler