code: def extract_pixels(X):
          
          if len(X.shape) != 4:
              raise ValueError('Array of input images has to be a 4-dimensional array of shape'
                               '[n_images, n_pixels_y, n_pixels_x, n_bands]')
  
          new_shape = (X.shape[0] * X.shape[1] * X.shape[2], X.shape[3],)
          pixels = X.reshape(new_shape)
          return pixels
docs: Extract pixels from array X
  
          :param X: Array of images to be classified.
          :type X: numpy array, shape = [n_images, n_pixels_y, n_pixels_x, n_bands]
          :return: Reshaped 2D array
          :rtype: numpy array, [n_samples*n_pixels_y*n_pixels_x,n_bands]
          :raises: ValueError is input array has wrong dimensions