class_docstr: This module implements :paper:`FPN`.
  It creates pyramid features built on top of some input feature maps.
class_docstr_tok: ["This","module","implements",":","paper",":","`","FPN","`",".","It","creates","pyramid","features","built","on","top","of","some","input","feature","maps","."]
code: def padding_constraints(self):
      return {"square_size": self._square_pad}
  
imports: import math
  import fvcore.nn.weight_init
  import torch
  import torch.nn.functional
  from torch import nn
  from detectron2.layers import Conv2d, ShapeSpec, get_norm
  from .backbone import Backbone
  from .build import BACKBONE_REGISTRY
  from .resnet import build_resnet_backbone
label_desc: Use image node_id 3 for calling the FPN obj's underlying member method code with example usage: obj.padding_constraints() and returns: dict