New submission from Gregory Beauregard <g...@greg.red>:
Currently, `typing.Annotated` (PEP 593) cannot be used at runtime with `typing.Final` and `typing.ClassVar` with `Annotated` on the outside: ``` from typing import Annotated, Final # TypeError: typing.Final[int] is not valid as type argument var: Annotated[Final[int], "foo"] = 4 ``` The only tenuously related mention of this I can find in a PEP is in PEP 593 (Annotated) which states "The first argument to Annotated must be a valid type". I believe the runtime behavior should be changed to allow any ordering for `Annotated` with `ClassVar` and `Final`. This was discussed in the typing-sig PEP 655 thread (TypedDict `Required` and `NotRequired`) where the current plan is to allow `Required`/`NotRequired` in any nesting order with `Annotated` while suggesting the `ClassVar`/`Final` ordering restriction be lifted: https://mail.python.org/archives/list/typing-...@python.org/message/22CJ5TJGIJ563D6ZKB7R3VUZXTZQND5X/ The argument for doing so is on the mailing list: https://mail.python.org/archives/list/typing-...@python.org/message/MPMOIBX3XFXCD4ZNDC6AV4CLSI5LN544/ To summarize: adopting an overly strict view of what constitutes a valid type for `Annotated` creates difficulties for people who use runtime introspection of `Annotated` annotations by requiring them to parse additional typing or field annotations (https://bugs.python.org/msg411067). This needlessly exacerbates tension between typing and non-typing uses of annotation space. In order to be a good citizen to other annotation users, the `Annotated` runtime ordering restriction should be lifted. ---------- messages: 411404 nosy: GBeauregard priority: normal severity: normal status: open title: typing: allow Annotated in outermost scope type: behavior versions: Python 3.10, Python 3.11, Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue46491> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
