On the other hand, you can list all packages using pm list packages.
I have no idea what is the difference between “system” and “system_ext”, and the description in the documentation seems vague.
，更多细节参见heLLoword翻译官方下载
Context manager that's used to automatically delete a queue when it's no，更多细节参见电影
Елизавета Городищева (Редактор отдела «Экономика»)