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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 get_merged_pianoroll(self, mode='sum'):
 """ Return the merged pianoroll. Parameters mode : {'sum', 'max', 'any'} A string that indicates the merging strategy to apply along the track axis. Default to 'sum'. - In 'sum' mode, the merged pianoroll is the sum of all the pianorolls. Note that for binarized pianorolls, integer summation is performed. - In 'max' mode, for each pixel, the maximum value among all the pianorolls is assigned to the merged pianoroll. - In 'any' mode, the value of a pixel in the merged pianoroll is True if any of the pianorolls has nonzero value at that pixel; False if all pianorolls are inactive (zero-valued) at that pixel. Returns ------- merged : np.ndarray, shape=(n_time_steps, 128) The merged pianoroll. """

        stacked = self.get_stacked_pianoroll()

        if mode == 'any':
            merged = np.any(stacked, axis=2)
        elif mode == 'sum':
            merged = np.sum(stacked, axis=2)
        elif mode == 'max':
            merged = np.max(stacked, axis=2)
        else:
            raise ValueError("`mode` must be one of {'max', 'sum', 'any'}.")

        return merged