code: def get_per_pixel_mean(names=('train', 'test', 'extra')):
          
          for name in names:
              assert name in ['train', 'test', 'extra'], name
          images = [SVHNDigit(x).X for x in names]
          return np.concatenate(tuple(images)).mean(axis=0)
docs: Args:
              names (tuple[str]): names of the dataset split
  
          Returns:
              a 32x32x3 image, the mean of all images in the given datasets