code: def get_max_length(self):
          
          max_length = 0
          for track in self.tracks:
              if max_length < track.pianoroll.shape[0]:
                  max_length = track.pianoroll.shape[0]
          return max_length
docs: Return the maximum length of the pianorolls along the time axis (in
          time step).
  
          Returns
          -------
          max_length : int
              The maximum length of the pianorolls along the time axis (in time
              step).