Terry, Gregory: The suggestion is not to change what 1 + "2" does, I fully agree that it behaves at it should. The suggestion is to change what ",".join(1, "2") does. There's no doubt that the intended result is "1, 2". That's why it's possible to coerce.

About the example with a list with mixed types: If the reason that example is buggy is "this list should only have strings", a better way to enforce that is to add types to enforces it.