foonelist.py

import collections.abc
import sys

class FooneList(collections.abc.MutableSequence):
    def __init__(self, *keys: str):
        self._store = sys._getframe(1).f_locals
        self._keys = keys

    def __getitem__(self, index):
        return self._store[self._keys[index]]

    def __setitem__(self, index, value):
        self._store[self._keys[index]] = value

    def __delitem__(self, index):
        key = self._keys[index]
        del self._keys[index]
        del self._store[key]

    def __len__(self):
        return len(self._store)

    def insert(self):
        raise TypeError("Cannot insert into a FooneList")


fl = FooneList('a', 'b', 'c')
fl[1] = 42
fl[2] = 69
fl[3] = "spam"
print(a, b, c)