os._Environ.get() and __contains__() raise and catch KeyError internally

Feature or enhancement

Proposal:

Since os._Environ is a subclass of collections.abc.Mapping, its get() and __contains__() methods are implemented in terms of __getitem__(). By forwarding to __getitem__(), a KeyError is raised when the key does not exist. This KeyError is then immediately caught and swallowed.

Handling this exception is extra, avoidable work. _Environ can check its internal dictionary directly which is more efficient.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-156492

從 issue 中描述的 os._Environ 的 get() 和 contains() 實作著手，檢查目前如何處理缺少的鍵。當這些方法避免引發並立即捕捉 KeyError，同時保留缺少鍵的現有結果時，此變更即告完成。