code: def _next_month(self):
          
          self._canvas.place_forget()
  
          year, month = self._date.year, self._date.month
          self._date = self._date + self.timedelta(
              days=calendar.monthrange(year, month)[1] + 1)
          self._date = self.datetime(self._date.year, self._date.month, 1)
          self._build_calendar()
docs: Update calendar to show the next month.