Thanks for the tip!
I'm on Orange Pi Zero running 4.10.1-sun8i
After importing pySerial, I tested this code:
port = serial.Serial("/dev/ttyS1", 115200, timeout=1)
Unfortunately it fails with 'serial.serialutil.SerialException: Could not configure port: (5, 'Input/output error')'
Listing the ports using: python -m serial.tools.list_ports , results in "no ports found"
I also tried adding the port using overlays as suggested in this post : https://forum.armbian.com/index.php?/topic/3651-uart-on-orange-pi-zero/#comment-26402
Any other suggestions?