<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_ds9(self, level="PREF"):
 """ Set the default values on the ds9 display. """

        self.set_zoom()
        ds9_settings = config.read("DS9."+level)
        for key in ds9_settings.keys():
            value = ds9_settings[key]
            cmd = key.replace("_", " ")
            self.ds9.set("{} {}".format(cmd, value))