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

从 issue 中描述的 os._Environ 的 get() 和 contains() 实现入手，检查当前如何处理缺失的键。当这些方法避免引发并立即捕获 KeyError，同时保留缺失键的现有结果时，此更改即告完成。