Append a Remind command generated from the iCalendar to the file

def append_vobject(self, ical, filename=None):
        """Append a Remind command generated from the iCalendar to the file"""
        if not filename:
            filename = self._filename
        elif filename not in self._reminders:
            return

        with self._lock:
            outdat = self.to_reminders(ical)
            open(filename, 'a').write(outdat)

        return Remind._get_uid(outdat)