Environment variable definitions file substitution does not work when debugging a Python file

[emptyVoid]

Environment data

• VS Code version: Code 1.34.0 (a622c65b2c713c890fcf4fbf07cf34049d5fe758, 2019-05-15T21:59:37.030Z)
• Extension version (available under the Extensions sidebar): 2019.4.12954
• OS and version: Windows x64 10.0.17763
• Python version (& distribution if applicable, e.g. Anaconda): 3.6
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): venv

Expected behaviour

According to documentation the value of any existing environment variable could be used when defining an environment variables.

Actual behaviour

Value of PATH environment variable is not being substituted.

Steps to reproduce:

1. Create .env file with a single line PATH="${PATH};Blah-blah-blah".
2. Print PATH value with print(os.environ.get('PATH'))
3. ;Blah-blah-blah gets printed.

[karrtikr]

Print PATH value with print(os.environ.get('PATH'))

How are you running this command. Are you using Run python file in terminal ,i.e running directly in terminal.
Or are you using the Python debugger (running by debugging). Resolution currently only works in debugger.

[emptyVoid]

I'm running it under debugger with this launch configuration:

{
    "name": "Python: Module",
    "type": "python",
    "request": "launch",
    "module": "blah",
    "console": "integratedTerminal"
}

[int19h]

This works if you do {env:PATH}.

However, this is not standard syntax. We should probably follow python-dotenv syntax on this: https://pypi.org/project/python-dotenv/

[luabud]

I opened microsoft/vscode-docs#3856 to track the documentation update that is required.

Related: microsoft/vscode-python#11812

[karrtikr]

This works if you do {env:PATH}.

@int19h This actually does not work if specified in a .env file. Weirdly it works when debugging a test via the debug launcher but not when debugging a Python file. I'm transferring this issue to debugpy as I believe it has its own environment variable resolver.

[int19h]

debugpy does not have its own variable substitution logic - it's entirely a VSCode thing. Ditto for "envfile" - debugpy expects to receive everything already fully expanded and substituted in "env".