Nested virtual environment support in site/venv modules

Feature or enhancement

Proposal:

It's a bit of a niche use case, but it would be helpful if you could have one virtual environment be created that references another as its parent. If you currently attempt to do this, the pyvenv.cfg of the child virtual environment only indirectly references the parent through the command variable (which doesn't appear to be used). The code in site.venv could be enhanced to infer the prefix of the parent environment and add those site packages after the current virtual environment. This would ensure that the order of sys.path entries would be appropriate.

This would allow you to create a group virtual environment with a lot of common packages and still allow users to have their own child environments with additional or newer packages.

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

从 issue 引用的 site.venv 实现所在的 Lib/site.py 开始，检查当前如何处理 pyvenv.cfg 和 command 变量。定义子环境应如何推断其父环境前缀，并将父环境的 site packages 排在子环境条目之后；当嵌套环境呈现预期的 sys.path 顺序时，即表示完成。