code: def start_editing(self, treeview, event):
          
          x, y = int(event.x), int(event.y)
          ret = treeview.get_path_at_pos(x, y)
          if not ret:
              return False
  
          path, column, cellx, celly = ret
  
          treeview.row_activated(path, Gtk.TreeViewColumn(None))
          treeview.set_cursor(path)
  
          return False
docs: Make the treeview grab the focus and start editing the cell
          that the user has clicked to avoid confusion with two or three
          clicks before editing a keybinding.
  
          Thanks to gnome-keybinding-properties.c =)