An alternate idea: convert the result of __divmod__ and __rdivmod__ to tuple instead raising an error. This will support the case of returning a list. I didn't implement this initially because I think this case is very unlikely occurred in real code.

Similar changes were made in past in PyMapping_Keys(). In Python 2 it just calls the keys() method and returns the result. In Python 3 it initially converted the result to list or tuple. But since the caller code often expects a list and use PyList API with the result, later PyMapping_Keys() was fixed but making it always returning a list.