In tkinter, `widget['foo'] = bar` and `widget.config(foo=bar)` do the same thing, but they will now type-check differently: the `widget['foo'] = bar` syntax allows 'foo' to be any string (e.g. a variable, not necessarily a Literal) and bar to be any object, while `widget.config(foo=bar)` checks the existence of the option and the type of bar. Similarly, cget takes a Literal argument but __getitem__ takes a string.
Testing script can still be found at https://github.com/python/typeshed/pull/4363/commits/c42a72c53e552ab501455def07017181f0158e80
Akuli