Add a `default` argument to `operator.attrgetter` and `operator.itemgetter`

Feature or enhancement

Proposal:

The proposal if for these functions to receive a default argument.

The main motivation is operator.attrgetter, which implements nested attribute access, but is missing getattr's default value support. operator.itemgetter also gets the default argument for consistency.

For operator.attrgetter, only AttributeErrors should be suppressed, and for operator.itemgetter, KeyError.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/enhancing-getattr-to-support-nested-attribute-access-with-dotted-strings/74305/12

先檢視針對 operator.attrgetter 和 operator.itemgetter 提議的行為，接著閱讀連結的 Discourse 討論，以了解尚未解決的設計問題。追蹤這兩個函式現有的實作和測試；完成的標準是支援預設引數，同時僅對 attrgetter 抑制 AttributeError，僅對 itemgetter 抑制 KeyError。