docstr: Args:
      x: Tensor of shape (N,C,H,W).
code: def forward(self, feats):
      """
      Args:
          x: Tensor of shape (N,C,H,W).
      """
      features = feats[0]
      results = []
  
      for stage in self.stages:
          results.append(stage(features))
  
      top_block_in_feature = results[-1]
      results.append(self.top_block(top_block_in_feature))
      assert self.num_levels == len(results)
  
      return results
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  import numpy
  import math
  from paddle import ParamAttr
  from paddle.regularizer import L2Decay
  from paddle.nn.initializer import Constant, TruncatedNormal
  from ppdet.modeling.shape_spec import ShapeSpec
  from ppdet.core.workspace import register, serializable
  from .transformer_utils import zeros_, DropPath, Identity, window_partition, window_unpartition
  from ..initializer import linear_init_
label_desc: Use image node_id 4 for calling the SimpleFeaturePyramid obj's underlying member method code with example usage: obj.forward(feats) and returns: results