code: def scroll_constrain (self):
          '''This keeps the scroll region within the screen region.'''
  
          if self.scroll_row_start <= 0:
              self.scroll_row_start = 1
          if self.scroll_row_end > self.rows:
              self.scroll_row_end = self.rowf scroll_constrain (self):
          '''This keeps the scroll region within the screen region.'''
  
          if self.scroll_row_start <= 0:
              self.scroll_row_start = 1
          if self.scroll_row_end > self.rows:
              self.scroll_row_end = self.rows
docs: This keeps the scroll region within the screen region.