class_docstr: Focus width and height information into channel space, used in YOLOX.
code: def forward(self, inputs):
      # inputs [bs, C, H, W] -> outputs [bs, 4C, W/2, H/2]
      top_left = inputs[:, :, 0::2, 0::2]
      top_right = inputs[:, :, 0::2, 1::2]
      bottom_left = inputs[:, :, 1::2, 0::2]
      bottom_right = inputs[:, :, 1::2, 1::2]
      outputs = paddle.concat(
          [top_left, bottom_left, top_right, bottom_right], 1
      )
      return self.conv(outputs)
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle import ParamAttr
  from paddle.regularizer import L2Decay
  from ppdet.core.workspace import register, serializable
  from ppdet.modeling.initializer import conv_init_
  from ..shape_spec import ShapeSpec
label_desc: Use image node_id 2 for calling the Focus obj's underlying member method code with example usage: obj.forward(inputs) and returns: self