code: def forward(self, feats, targets=None):
      assert len(feats) == len(
          self.fpn_strides
      ), "The size of feats is not equal to size of fpn_strides"
  
      if self.training:
          return self.forward_train(feats, targets)
      else:
          return self.forward_eval(feats)
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from ppdet.core.workspace import register
  from ..losses import ProbIoULoss
  from ..initializer import bias_init_with_prob, constant_, normal_, vector_
  from ppdet.modeling.backbones.cspresnet import ConvBNLayer
  from ppdet.modeling.ops import get_static_shape, get_act_fn, anchor_generator
  from ppdet.modeling.layers import MultiClassNMS
label_desc: Use image node_id 5 for calling the PPYOLOERHead obj's underlying member method code with example usage: obj.forward(feats, targets) and returns: self, self