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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def play_Composition(self, composition, channels=None, bpm=120):
 """Play a Composition object."""

        self.notify_listeners(self.MSG_PLAY_COMPOSITION, {'composition'
                              : composition, 'channels': channels, 'bpm': bpm})
        if channels == None:
            channels = map(lambda x: x + 1, range(len(composition.tracks)))
        return self.play_Tracks(composition.tracks, channels, bpm)