New submission from Pablo Aguilar <pablo.agui...@fatec.sp.gov.br>:
Hey, I'm not sure if this is really a bug but I'd like to show to prevent some undesired behavior! I'm working in the `match` support for returns (https://github.com/dry-python/returns) library when I saw a behavior similar to the described in `Constant Value Patterns` section on PEP-622 (https://www.python.org/dev/peps/pep-0622/#constant-value-patterns). A very small and reproducible example: ```python from typing import Any, ClassVar, Optional class Maybe: empty: ClassVar['Maybe'] _instance: Optional['Maybe'] = None def __new__(cls, *args: Any, **kwargs: Any) -> 'Maybe': if cls._instance is None: cls._instance = object.__new__(cls) return cls._instance Maybe.empty = Maybe() if __name__ == '__main__': my_maybe = Maybe() match my_maybe: case Maybe.empty: print('FIRST CASE') case _: print('DEFAULT CASE') ``` The output here is `FIRST CASE`, but if I delete `__new__` method the output is `DEFAULT CASE`. Is that the correct behavior? Python version: 3.10.0a7 ---------- components: Interpreter Core messages: 397380 nosy: thepabloaguilar priority: normal severity: normal status: open title: Undesired Behavior on `match` using Singleton object type: behavior versions: Python 3.10 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue44617> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
