Ultimately, I wanted to extend the dataclasses.dataclass and collections.Mapping because I wanted to make dataclasses that I can use ** operator on with some additional functions. Since dataclass is a function, not a class, I couldn't use inheritance. So I made a new wrapping function from dataclasses import dataclass as original_dataclass, fields from collections import Mapping from typing import Any, Generator, Type def __iter__(self) -> Generator[str, None, None]: for field in fields(self): yield field.name def __len__(self) -> int: return len(fields(self)) def __getitem__(self, item: Any) -> Any: return getattr(self, item) def additional_function(self): print("Yes") def dataclass(cls: Type) -> Type: cls.additional_function = additional_function cls.__iter__ = __iter__ cls.__len__ = __len__ cls.__getitem__ = __getitem__ # If `cls` has these methods, then it counts as a Mapping in the python world for method in ("__contains__", "keys", "items", "values", "get", "__eq__", "__ne__"): setattr(cls, method, getattr(Mapping, method)) return original_dataclass(cls) @dataclass class MyNewClass: hello: str # usage def usecase_function(hello:str): pass new_class = MyNewClass("hi") usecase_function(**new_class) # <- vs-code complains here new_class.hello # <- vs-code complains here The python interpreter(3.8.13) does not throw an error. However, my editor, vs-code is complaining that this is not a Mapping. I assume because I return a mere Type as the return of the new dataclass function. So I annotate the return as Type[Mapping]. Now, vs-code complains that new_class doesn't have the attribute hello. I assume because dataclass returns a Type[Mapping] which doesn't have a hello attribute. But I don't know how to annotate the function dataclass in this situation. Does anyone know how to annotate in this situation? Thank you. Continue reading...
