Embedded interpreters: No way to extend `sys.path`

Feature or enhancement

Proposal:

Setting up an embedded Python interpreter often involves augmenting sys.path with some application-specific subdirectories, so as not to pollute the system's normal Python installation.

Unfortunately, PyConfig only affords either replacing the default path wholesale, or leaving it as-is (via module_search_paths_set). There appears to be no way to augment sys.path with application-specific directories and no documented way to retrieve the default contents of sys.path.

A workable solution might be to enhance cfg.module_search_paths_set so that when it's set to 2 or 3, the application's paths shall be prepended / appended to sys.path instead of replacing it.

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/embedding-how-do-i-extend-sys-path/75734

先閱讀 PyConfig 文件以及 issue 中描述的 module_search_paths_set 行為，然後閱讀連結的 Discourse 討論，了解先前的設計背景。確定應如何將應用程式專用路徑與預設的 sys.path 結合，以及文件中應如何描述 API 行為；完成內容應包括已達成共識的實作，以及相應的文件或測試。