code: def forward(self, blocks, for_mot=False):
      if self.use_trans:
          last_feat = blocks[-1]
          n, c, h, w = last_feat.shape
  
          # flatten [B, C, H, W] to [B, HxW, C]
          src_flatten = last_feat.flatten(2).transpose([0, 2, 1])
          if self.eval_size is not None and not self.training:
              pos_embed = self.pos_embed
          else:
              pos_embed = self.build_2d_sincos_position_embedding(
                  w=w, h=h, embed_dim=self.hidden_dim
              )
  
          memory = self.encoder(src_flatten, pos_embed=pos_embed)
          last_feat_encode = memory.transpose([0, 2, 1]).reshape(
              [n, c, h, w]
          )
          blocks[-1] = last_feat_encode
  
      blocks = blocks[::-1]
      fpn_feats = []
  
      for i, block in enumerate(blocks):
          if i > 0:
              block = paddle.concat([route, block], axis=1)
          route = self.fpn_stages[i](block)
          fpn_feats.append(route)
  
          if i < self.num_blocks - 1:
              route = self.fpn_routes[i](route)
              route = F.interpolate(
                  route, scale_factor=2.0, data_format=self.data_format
              )
  
      pan_feats = [
          fpn_feats[-1],
      ]
      route = fpn_feats[-1]
      for i in reversed(range(self.num_blocks - 1)):
          block = fpn_feats[i]
          route = self.pan_routes[i](route)
          block = paddle.concat([route, block], axis=1)
          route = self.pan_stages[i](block)
          pan_feats.append(route)
  
      return pan_feats[::-1]
  
imports: import math
  import copy
  import numpy
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from ppdet.core.workspace import register, serializable
  from ppdet.modeling.layers import DropBlock, MultiHeadAttention
  from ppdet.modeling.ops import get_act_fn
  from ..backbones.cspresnet import ConvBNLayer, BasicBlock
  from ..shape_spec import ShapeSpec
  from ..initializer import linear_init_
label_desc: Use image node_id 3 for calling the CustomCSPPAN obj's underlying member method code with example usage: obj.forward(blocks, for_mot) and returns: pan_feats