Update findPythonDeps

[Flamefire]

I noticed that the script failed to detect e.g. jupyter-core because the package_name entry is jupyter_core. However that isn't consistent:

• "PyQt5-sip": 'key': 'pyqt5-sip', 'package_name': 'PyQt5-sip'
• "jupyter-core": 'key': 'jupyter-core', 'package_name': 'jupyter_core'

I fixed that and used the opportunity to generally do some updates. In total:

• Require Python 3.3 3.6 (due to f-strings and subprocess.DEVNULL [3.3])
• Add/update documentation
• Use f-strings for formatted output
• Fix detecting packages where the name might appear as the "key" not the "package_name"
• Set PYTHONNOUSERSITE
• Use venv module instead of virtualenv to require less packages

This should make the script more robust and easier to understand and maintain. Especially the description at the top should be very helpful for those that don't know it yet.

I used PyLint to check the script. In one place there was an unused argument that should have been used but wasn't. Putting the "main" code into a function allowed to detect that as there are no more global variables.

[Micket]

Require Python 3.3

Typo (given that you use f-strings, so it would be python3.6 at least)?

[Flamefire]

Typo (given that you use f-strings, so it would be python3.6 at least)?

Yes, wasn't aware that f-strings were so late. Also the change from virtualenv to venv wasn't complete.

The script will (also) be run with a loaded Python module. So after this change it can no longer be used to find packages for Python 2 or < 3.6. That is 2018b for Python2 and 2016b for Python 3.5. I'd say this is fine as there is likely no one adding ECs for those.