code: def register_calendar(self, name, calendar, force=False):
          
          if force:
              self.deregister_calendar(name)
  
          if self.has_calendar(name):
              raise CalendarNameCollision(calendar_name=name)
  
          self._calendars[name] = calendar
docs: Registers a calendar for retrieval by the get_calendar method.
  
          Parameters
          ----------
          name: str
              The key with which to register this calendar.
          calendar: TradingCalendar
              The calendar to be registered for retrieval.
          force : bool, optional
              If True, old calendars will be overwritten on a name collision.
              If False, name collisions will raise an exception.
              Default is False.
  
          Raises
          ------
          CalendarNameCollision
              If a calendar is already registered with the given calendar's name.