Problem solved
For some reason the refechtEvent is not available on the calendar object. Which seems a bit weird because I import the full library.
I have debugged this by printing the classes / functions of the calendar object.
The print(dir()) shows all the available methods on the python object.
Seeing the available options I have solved this by removing the event and added the new event. event.remove() and self.calendarObj.addEvent({...})
To activate an onclick via python add the following property to your calendar object
...
'eventClick': self.event_calender_clicked,
...
The self.event_calender_clicked accepts a second parameter which hold all the information about the clicked event. def event_calender_clicked(self, info): ...
printing the classes and functions can be done via print(dir(self.my_javscript_obj))
It’s a very handy debug function the dir() and I’m using it now for every javascript library to see all my options.