old_contents: from .model import Model
  from ...api import layerize
  from .affine import Affine
  
  
  class Residual(Model):
      def __init__(self, layer):
          Model.__init__(self)
          self._layers.append(layer)
          self.on_data_hooks.append(on_data)
  
      def __call__(self, X):
          return X + self._layers[0](X)
  
      def begin_update(self, X, drop=0.):
          y, bp_y = self._layers[0].begin_update(X, drop=drop)
          output = X+y
          def residual_bwd(d_output, sgd=None):
              return d_output + bp_y(d_output, sgd)
          return output, residual_bwd
  
  def on_data(self, X, y=None):
      for layer in self._layers:
          for hook in layer.on_data_hooks:
              hook(layer, X, y)
          if hasattr(layer, 'W'):
              layer.W.fill(0)
  
new_contents: from .model import Model
  from ...api import layerize
  from .affine import Affine
  
  
  class Residual(Model):
      def __init__(self, layer):
          Model.__init__(self)
          self._layers.append(layer)
          self.on_data_hooks.append(on_data)
  
      def __call__(self, X):
          Y = self._layers[0](X)
          if isinstance(X, list) or isinstance(X, tuple):
              return [X[i]+Y[i] for i in range(len(X))]
          else:
              return X + Y
  
      def begin_update(self, X, drop=0.):
          y, bp_y = self._layers[0].begin_update(X, drop=drop)
          if isinstance(X, list) or isinstance(X, tuple):
              output = [X[i]+y[i] for i in range(len(X))]
          else:
              output = X+y
          def residual_bwd(d_output, sgd=None):
              dX = bp_y(d_output, sgd)
              if isinstance(d_output, list) or isinstance(d_output, tuple):
                  return [d_output[i]+dX[i] for i in range(len(d_output))]
              else:
                  return d_output + dX
          return output, residual_bwd
  
  def on_data(self, X, y=None):
      for layer in self._layers:
          for hook in layer.on_data_hooks:
              hook(layer, X, y)
          if hasattr(layer, 'W'):
              layer.W.fill(0)
  
subject: Make residual connections work for list-valued inputs