Thanks a lot, this saved a lot. Two (minor) issues remained:
1) my Rankforce 2310 is using an+ special kind of USB chip the Raspbian OS binds as /dev/usb/hiddev0 instead of the standard USB /dev/ttyUSB0 or similar. A "port = /dev/ttyUSB0" is necessary.
2) Barometer and Wind speed / direction shows N/A on the web page. The debug data are correct. - some idea?
Anyway I keep looking for the solution. I started to convert the python2 to python3 code, but problem is persistent.
Greetings