'Set the current calendar
@param name: the name of the calendar (falls back to CALENDAR)'

def _set_calendar(self, name=None):

    calendars = self._calendars
    if (name not in calendars):
        name = self.CALENDAR
    if (name == self.CALENDAR):
        calendar = self
    else:
        calendar = calendars[name](name)
    self._name = name
    self._calendar = calendar
    return calendar
