code: def clear_data(self):
          
          self.tab = None
          self.cols = []
          self._idx = []
          self.x_col = ''
          self.y_col = ''
          self.w.xcombo.clear()
          self.w.ycombo.clear()
          self.w.x_lo.set_text('')
          self.w.x_hi.set_text('')
          self.w.y_lo.set_text('')
          self.w.y_hi.set_text('')
docs: Clear comboboxes and columns.