<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def save(self):
 """ Save this prefix to persistent storage Returns: None """

        if not os.path.exists(self.paths.virt()):
            os.makedirs(self.paths.virt())

        self._save_metadata()
        self.virt_env.save()