code: def __init__(
      self,
      in_channels=256,
      out_channels=(
          [256, 512],
          [256, 512],
          [128, 256],
          [128, 256],
          [128, 256],
      ),
      strides=(2, 2, 2, 1, 1),
      paddings=(1, 1, 1, 0, 0),
  ):
      super(SSDExtraHead, self).__init__()
      self.convs = nn.LayerList()
      for out_channel, stride, padding in zip(
          out_channels, strides, paddings
      ):
          self.convs.append(
              self._make_layers(
                  in_channels,
                  out_channel[0],
                  out_channel[1],
                  stride,
                  padding,
              )
          )
          in_channels = out_channel[-1]
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from ppdet.core.workspace import register
  from paddle.regularizer import L2Decay
  from paddle import ParamAttr
  from ..layers import AnchorGeneratorSSD
  from ..cls_utils import _get_class_default_kwargs
label_desc: Use image node_id 1 to create a new SSDExtraHead object from inherited base classes: nn with example: obj = SSDExtraHead(in_channels, out_channels, strides, paddings)