<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def buttons_pressed(self, channel=1):
 """ Returns list of currently pressed buttons. Note that the sensor can only identify up to two buttons pressed at once. """

        self._ensure_mode(self.MODE_IR_REMOTE)
        channel = self._normalize_channel(channel)
        return self._BUTTON_VALUES.get(self.value(channel), [])