How do you influence a VSCode launch environment?

launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Launch",
            "type": "debugpy",
            "request": "launch",
            "program": "${file}",
            "console": "integratedTerminal"
        }
    ]
}

launch.py

import os

if __name__ == '__main__':
    if 'HOW_DID_THIS_GET_HERE' in os.environ:
        print(os.environ['HOW_DID_THIS_GET_HERE'])
    else:
        print('missing environment variable')