Serhiy Storchaka <storchaka+cpyt...@gmail.com> added the comment:
I have created an alternative PR 31143 which adds special method __typing_subst__ in TypeVar and ParamSpec instead of __parameters__ and __getitem__. It has almost the same effect except making TypeVar and ParamSpec and subscriptable. The Python code in typing.py and _collections_abc.py is simplified, but the C code is little changed. But on other hand, the reasons for PR 27511: 1. We already implemented __getitem__ for a Concatenate alias, although it is never documented. It is not even necessary, it is a pure implementation detail which makes the code for nested variables substitution simpler. Adding __parameters__ and __getitem__ in TypeVar and ParamSpec would have the same effect on simplification of the code. 2. There is a use case for subscription of TypeVar. For example: if version < 2: RetType = T elif version < 3: RetType = Optional[T] else: RetType = Optional[T] | Literal[Unknown] def get_int(precision: int) -> RetType[int]: ... def get_str(encoding: str) -> RetType[str]: ... def get_any(converter: Callable[[str], T]) -> RetType[T]: ... ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue44796> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
