class ChainedDicts(dict):
    def __init__(self, *dicts):
        self.dicts = dicts
        self.base = {}

    def __getitem__(self, item):
        if item in self.base:
            return self.base[item]
        elif item not in self.dicts[0]:
            raise KeyError
        for internal_dict in self.dicts:
            if item in internal_dict:
                item = internal_dict[item]
            else:
                return item
        return item

    def __setitem__(self, key, value):
        self.base[key] = value


    def __delitem__(self, key):
        if key in self.base:
            del self.base[key]
        if key in self.dicts[0]:
            del self.dicts[0][key]


d = ChainedDicts({1: 2, 3: 4}, {4: 5, 6: 8})

print(d[1])
print(d[3])