<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def enter_command_mode(self):
 """ Go into command mode. """

        self.application.layout.focus(self.command_buffer)
        self.application.vi_state.input_mode = InputMode.INSERT

        self.previewer.save()