example.py

@property
def history(self):
        """Return all records in the History list"""
        return self._history

def undo(self):
        """Undo a command if there is a command that can be undone.
        Update the history psoition so that further UNDOs or REDOs
        point to the correct index"""
        if self._history_position > 0:
            self._history_position -= 1
            self._commands[
                self._history[self._history_position][1]
            ].execute(self._history[self._history_position][2])
        else:
            print("nothing to undo")

def redo(self):
        """Perform a REDO if the history_position is less than the end of the history list"""
        if self._history_position + 1 < len(self._history):
            self._history_position += 1
            self._commands[
                self._history[self._history_position][1]
            ].execute(self._history[self._history_position][2])
        else:
            print("nothing to REDO")