Working example of Python upload with API v3?

Anybody managed to do client auth with API v3 and Python? Even Mapillary themselves use the old v2 login in their uploader.
I tried the usual thing here but it did not work:
https://requests-oauthlib.readthedocs.io/en/latest/oauth2_workflow.html#backend-application-flow
Some sample code to get the bearer would be great.

I found out that the API v3 auth implementation is very limited and just allows web and mobile auth. So I did this as a workaround to gain the access token:
https://github.com/moenk/mapillary-code/blob/master/python3/accesstoken3.py
Maybe there will be a tiny uploader later to upload images to Mapillary with Python 3.