TypeIs for isinstance

Apologies if I'm missing something obvious, but I checked issues and PR's and haven't seen this mentioned explicitly.

Could isinstance use TypeIs?

With multiples checks it could return an union, with one type T a TypeIs[T].

I often find myself writing one-liner helpers functions that just call isinstance, see this script for example:

https://github.com/OutSquareCapital/pyochain/blob/master/scripts/check_docstrings.py

This both add boilerplate and a performance tax due to a double function call overhead.

I'm very often using lambdas with fluent interfaces, e.g

res = (
my_iterator
.map(lambda x: ...)
.filter(lambda x: isinstance(x, int)
)

Assuming my_iterator is an Iterator[Any], it would be fantastic if it could be narrowed to Iterator[int] without having to define a separate TypeIs function.

リンクされている scripts/check_docstrings.py の例と、要求されている isinstance/TypeIs の動作から始めます。単一のチェックと複数のチェックで型をどのように絞り込むべきかを明確にし、その動作を検証するために必要な typeshed のスタブとテストを特定します。提案に明確な型付け結果と対応するカバレッジが定義されていれば完了です。