`None` vs `Never` as `typing.Generator`'s send type

Documentation

Documentation for typing.Generator currently says:

If your generator will only yield values, set the SendType and ReturnType to None

While not obviously wrong, using None as SendType looks imprecise: we want a typechecker to warn about .send(t) calls for any t, right? Using that method likely indicates that the generator is used incorrectly.

Now type checkers will reject .send(t) calls for all t types except None and Any.

Since python 3.11 we have a Never type - effectively a "please don't" type. So setting SendType to Never instead of None would be more useful from the interface declaration perspective: literally saying "please don't send anything here".

I do understand that None is there to match runtime behaviour closer since calling it.send(None) is equivalent to calling next(it) for the next time, so None is formally correct. However, there's no benefit ever from doing it.send(None) if the generator does not use sent values - calling next(it) is clearly preferable.

My suggested solution is to recommend typing.Never as SendType in such cases in documentation. I'm ready to write a PR with this change.

從連結的 typing.Generator 文件開始，檢視 SendType 和 ReturnType 的指引。在繼續之前檢查包含五則留言的討論，因為該 issue 最近沒有活動。對於不接受傳送值的產生器，文件反映已解決的建議即表示完成。