> Python cannot express this relationship with type annotations. What relationship? That two classes which have no ancestor classes in common happen to be duck

> Python cannot express this relationship with type annotations. What relationship? That two classes which have no ancestor classes in common happen to be duck type compatible? Yes, Python type annotations can't express that, because there is no type relationship to express. The way to avoid this problem in Python is to make sure duck type compatible classes have an ancestor class in common. That was a main point of the collections.abc module when it was introduced, to provide actual classes that expressed the duck types that were built into Python (being a subclass of MutableMapping, for example, expresses the fact that a class is duck type compatible with the built-in dict class). As for "dataclass", it's not a class, it's a function. But the dataclass module provides the "is_dataclass" function that you can call on any class to check whether it's a dataclass. As far as I know, this will detect both your "dataclass_alias" and "dataclass_wrapper" cases. So this function could be used by any tool that wants to check for dataclasses.