Explain once and for all how to set python.pythonPath using environment variables or remove this from docs

[smac89]

Environment data

• VS Code version: 1.44.0
• Extension version (available under the Extensions sidebar): 2020.2.64397
• OS and version: Linux x64 5.5.8-arch1-1
• Python version: Virtual env python 2.7
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): Pipenv
• Jedi or Language Server?: disabled
• Value of the python.languageServer setting: Microsoft

Expected behaviour

From reading the docs, it seems to suggest that one can set python.pythonPath using environment variable.

I have a .env file with the content:

PYTHON_INSTALL_LOC="/home/chigozirim/dev/virtualenvs/XXX/bin/python"

And I have set the value of python.pythonPath using:

"python.pythonPath": "${env:PYTHON_INSTALL_LOC}"

I expect the plugin to pick up the actual path from the environment variable and use that python

Actual behaviour

The plugin fails to see the python I specified and instead picks up the system default python, which means the variable is resolving to an empty string

Steps to reproduce:

Use my setup above, with the .env file.

Directory structure

➜ tree -aL 1
.
├── data
├── .env
├── fig
├── .git
├── .gitignore
├── mnist
├── Pipfile
├── Pipfile.lock
├── .pylintrc
├── README.md
├── run.ps1
├── src
└── .vscode

Logs

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

[Info  - 6:41:44 p.m.] Analysis cache path: /home/chigozirim/.cache/Microsoft/Python Language Server
[Info  - 6:41:44 p.m.] Microsoft Python Language Server version 0.5.31.0
[Info  - 6:41:44 p.m.] Workspace root: /home/chigozirim/projects/neural-networks-and-deep-learning-py
[Info  - 6:41:44 p.m.] GetCurrentSearchPaths /usr/bin/python 
[Info  - 6:41:44 p.m.] Interpreter search paths:
[Info  - 6:41:44 p.m.]     /usr/lib/python3.8
[Info  - 6:41:44 p.m.]     /usr/lib/python3.8/lib-dynload
[Info  - 6:41:44 p.m.]     /home/chigozirim/.local/lib/python3.8/site-packages
[Info  - 6:41:44 p.m.]     /usr/lib/python3.8/site-packages
[Info  - 6:41:44 p.m.] User search paths:
[Info  - 6:41:44 p.m.]     /home/chigozirim/projects/neural-networks-and-deep-learning-py/src
[Info  - 6:41:47 p.m.] Initializing for /usr/bin/python
[Info  - 6:41:47 p.m.] Analysis caching mode: None.

In case I'm not making myself clear, I am referring to where it states in the docs:

By default, the Python extension looks for and loads a file named .env in the current workspace folder, then applies those definitions. The file is identified by the default entry "python.envFile": "${workspaceFolder}/.env" in your user settings (see General settings). You can change the python.envFile setting at any time to use a different definitions file.

I'm certain this means that the extension is supposed to read the .env file and use the values found there. If that's the case, why does it fail to use the environment variables I set, to fill in python.pythonPath?

I just need to know if this feature is supported or not and what the docs means when it specifies the use of environment variables for setting the python.pythonPath. If this is actually not supported, then I strongly suggest it should be, otherwise it should not be in the docs so that devs are not being misled and end up wasting time on something that wasn't supposed to work.

See also:
#944 (comment)

[ericsnowcurrently]

@smac89, thanks for getting in touch with us about this. We'll get back to you as soon as possible.

[ghost]

I think I'm facing the same issue.
I want to add sub-folders to the PYTHONPATH, to import python files in the same folder.
I'm using .env file and the Pylint and python-debugger recognize the .env file, but when I try to run the file in python run Current file in python interactive window or run python file in terminal the python throw ModuleNotFoundError

[ericsnowcurrently]

@smac89, I was able to verify the behavior as described: any setting using an environment variable defined only in a .env file is effectively ignored. Note that this has always been the case. Also note that env var substitution works as documented for regular environment variables (not in .env file).

The cause is that the extension code which applies environment variables in settings does not currently use those defined in .env files. In fact, .env files are currently only used when the extension creates subprocesses or new terminals.

The resolution of the problem you've encountered is one of the following:

1. apply the .env file when doing variable substitution
2. update the docs to clarify that env var substitution in settings ignores .env files
3. do nothing

We'll look into which makes the most sense.

[smac89]

Thanks @ericsnowcurrently
Hopefully decision number 1 is taken, because it will prove to be the most useful seeing as support for .env is already popular among virtualenv enthusiasts and already has complete support by pipenv. It is also easy to add support, as you just need to source .env in a bash-like environment, or simply load it with python-dotenv or environs

[luabud]

Thanks for bringing this up! We'll update the docs accordingly. FWIW, we're also deprecating the python.pythonPath setting (#2125).

Closing in favour of microsoft/vscode-docs#3550 and #11015.