code: def __focus(self, item):
          
          cols = self.__get_display_columns()
          for col in cols:
              self.__event_info =(col,item)
              self.event_generate('<<TreeviewInplaceEdit>>')
              if col in self._inplace_widgets:
                  w = self._inplace_widgets[col]
                  w.bind('<Key-Tab>',
                      lambda e: w.tk_focusNext().focus_set())
                  w.bind('<Shift-Key-Tab>',
                      lambda e: w.tk_focusPrev().focus_set())
docs: Called when focus item has changed