Which is the official python library for comunications with UR robots?
tldr - there isnt one.
Universal Robots has an unofficially-official package for RTDE in python: GitHub - UniversalRobots/RTDE_Python_Client_Library: RTDE client library and examples
There is a decent third party project over here: GitHub - SintefManufacturing/python-urx: Python library to control a robot from 'Universal Robots' http://www.universal-robots.com/
and ur_rtde: ur-rtde ยท PyPI
and finally, there is a paid library from Under Automation, but I havent used it so i cant speak on it: GitHub - underautomation/UniversalRobots: UnderAutomation Universal Robots Communication SDK (Software Development Kit) provides the ability to create customized applications that can communicate with every UR robots.