shutil: Inconsistent return types when using pathlib

Bug report

Bug description:

Using pathlib with shutil usually works, but there are some quirks when it comes to return types. As an example, see the copy function (but other functions are affected as well):

https://github.com/python/cpython/blob/67ded6a4faae29edff8e4f7886978e71ce116e33/Lib/shutil.py#L468-L484

In this case, if a Path object gets passed in as dst, it will be returned unchanged if it is not a directory, but a str will be returned if it is a directory. That's unexpected, the return type should be consistent, probably by always returning a str.

I assume that pathlib support is mostly incidental in shutil, considering that the latter predates the former. shutil should probably be reviewed for proper pathlib support at some point. (See also a few other pathlib/shutil related issues reported here.)

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-132820

先檢查連結的 PR gh-132820，然後檢視 Lib/shutil.py 中 copy 附近的程式碼，以及報告中提到的其他 pathlib 相關函式。檢查現有的 shutil 測試，並確保受影響的函式具有一致且有文件說明的回傳型別，同時使用測試涵蓋作為目錄和不作為目錄的 Path 目的地。