code: def transpose(self, semitone):
          
          if semitone > 0 and semitone < 128:
              self.pianoroll[:, semitone:] = self.pianoroll[:, :(128 - semitone)]
              self.pianoroll[:, :semitone] = 0
          elif semitone < 0 and semitone > -128:
              self.pianoroll[:, :(128 + semitone)] = self.pianoroll[:, -semitone:]
              self.pianoroll[:, (128 + semitone):] = 0
docs: Transpose the pianoroll by a number of semitones, where positive
          values are for higher key, while negative values are for lower key.
  
          Parameters
          ----------
          semitone : int
              The number of semitones to transpose the pianoroll.