<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_prompt(self, prompt_command="", position=0):
 """ writes the prompt line """

        self.description_docs = u'{}'.format(prompt_command)
        self.cli.current_buffer.reset(
            initial_document=Document(
                self.description_docs,
                cursor_position=position))
        self.cli.request_redraw()