Yeah, that gives me the heebie jeebies. Fair enough if you want to use magic comments for an entirely third-party system like MyPy, but using them for a built-i

Yeah, that gives me the heebie jeebies. Fair enough if you want to use magic comments for an entirely third-party system like MyPy, but using them for a built-in language feature feels wrong. Besides, how necessary is it? Presumably those constrained types can be instantiated: x = Dict[str, str]() The constrained type's __new__ would be annotated appropriately, and return an ordinary dict. It's a bit less "pure" in that this is no longer strictly an annotation, but I'd much prefer that bit of impurity than magic comments.