code: def forward(self, x):
      if self.stride > 1:
          x1 = self.branch1(x)
          x2 = self.branch2(x)
      else:
          x1, x2 = x.chunk(2, axis=1)
          x2 = self.branch2(x2)
      out = paddle.concat([x1, x2], axis=1)
      out = channel_shuffle(out, groups=2)
      return out
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from numbers import Integral
  from paddle import ParamAttr
  from paddle.regularizer import L2Decay
  from paddle.nn.initializer import Normal, Constant
  from ppdet.core.workspace import register
  from ppdet.modeling.shape_spec import ShapeSpec
  from ppdet.modeling.ops import channel_shuffle
  from ..None import layers
label_desc: Use image node_id 2 for calling the ShuffleUnit obj's underlying member method code with example usage: obj.forward(x) and returns: out