Fail to use an environment variable in `python.defaultInterpreterPath` on Windows

[wdscxsj]

Environment data

• VS Code version: 1.43.1
• Extension version (available under the Extensions sidebar): 2020.3.69010
• OS and version: Windows 10 64-bit
• Python version: 3.8.2

Expected behaviour

An environment variable in python.pythonPath is respected across all platforms.

Actual behaviour

Works on Linux (via Remote SSH), but fails on Windows.

Steps to reproduce:

1. Specify "python.pythonPath": "{env:PYTHON_FOR_VSCODE}" in settings.json.
2. Set a Windows environment variable PYTHON_FOR_VSCODE to point to an installed Python interpreter, in my case C:\Tools\Python3\python.exe.
3. Restart VSCode, and open a hello.py.
4. The yellow prompt "Select Python Interpreter" persists.
   • When it's clicked, a combobox comes to say current: {env:PYTHON_FOR_VSCODE}, and lists my locally installed Python interpreters, including C:\Tools\Python3\python.exe. Choosing it works fine, but defeats the purpose of using an environment variable.
   • In VSCode's Terminal, %PYTHON_FOR_VSCODE% --version runs as expected.

[karrtikr]

Hi @wdscxsj 👋
We're deprecating python.pythonPath setting with #10375, moving it out of settings, so we don't plan to support this enhancement.

I am assuming you're using environment variables here as you don't want to commit your pythonPath to source control. We plan to store settings in a VSCode storage instead of settings.json files, so you should no longer face this once #10375 gets in. Closing this in favor of that.

[wdscxsj]

@karrtikr OK... Actually my setting "python.pythonPath": "{env:PYTHON_FOR_VSCODE}" was intended to select the preconfigured "default Python" for each machine my VSCode could connect to. It covers the folder/project mode as well as the single file case. Will #10375 work in both cases?

[karrtikr]

I see. In that case, consider the workaround:

If no interpreter is specified in settings, we check the PATH environment variable to autoselect the interpreter. You can append the preconfigured "default Python" to PATH environment variable instead of storing it in PYTHON_FOR_VSCODE, and it'll automatically be picked up if don't have python.pythonPath present in settings.

[wdscxsj]

Sure, that's good enough. Actually it's been a surprise to me that the first Python on PATH is not automatically picked.

[karrtikr]

I just realized that the original bug you described will still be applicable for #10375 . I am reopening the issue and changing the title accordingly.