I have a class that behaves like a wrapper around some object. The object will always be a subclass of some parent class, but otherwise it can be anything (to simplify, I assume this parent class is object in my example). Therefore, I made the Wrapper class generic. I now want to have a dict that maps some objects classes to their corresponding wrapper class. The wrapper will always correspond, no issubclass check (or similar) needed from a runtime perspective. As far as I can tell, it is not even possible, because I use some generic method to perform the mapping. I would like to reflect this in my type hints, i.e. the type checker should only allow key-value-pairs with types type[SomeObject], type[Wrapper[SomeObject]]. This is mostly relevant when accessing the dict, if I access the value for the key SomeObject, then the result should be type narrowed to Wrapper[SomeObject]. TypeVars do not work for me though (and I assume they are not intended for this use case): wrapper_mapping: dict[type[T], type[Wrapper[T]]] # Does not work Is it even possible with the current type hint system? How can I make the type checker happy, without using ignore comments? class Wrapper[T]: def __init__(self, thing: T): self.thing: T = thing class StringWrapper(Wrapper[str]): def __init__(self, thing: str): thing += "!!!" super().__init__(thing) wrapper_mapping = {str: StringWrapper, int: Wrapper[int]} def wrap[T](thing: T) -> Wrapper[T]: # A lot of type checker warnings, but works at runtime return wrapper_mapping[type(thing)](thing) print(wrap("hello").thing) # hello!!! print(wrap(2).thing) # 2 mypy-playground basedpyright-playground Continue reading...
