@property
    def summary(self):
        bday = self._vevents[self.ref].get('x-birthday', None)
        if bday:
            number = int(bday[:4]) - self.start_local.year
            name = self._vevents[self.ref].get('x-fname', None)
            return '{name}\'s {number}th birthday'.format(name=name, number=number)
        else:
            return self._vevents[self.ref].get('SUMMARY', '')
dataset/ETHPy150Open pimutils/khal/khal/khalendar/event.py/Event.summary/swapped operands of `-`