code: def get_pane_index(self, pane):
          " Return the index of the given pane. ValueError if not found. "
          assert isinstance(pane, Pane)
          return self.panes.index(panef get_pane_index(self, pane):
          " Return the index of the given pane. ValueError if not found. "
          assert isinstance(pane, Pane)
          return self.panes.index(pane)
docs: Return the index of the given pane. ValueError if not found.