code: def __init__(self, backbone, neck, head):
      super(RetinaNet, self).__init__()
      self.backbone = backbone
      self.neck = neck
      self.head = head
  
file_path: PaddleDetection/ppdet/modeling/architectures/retinanet.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from ppdet.core.workspace import register, create
  from .meta_arch import BaseArch
  import paddle
  import paddle.nn.functional
label_desc: Use image node_id 1 to create a new RetinaNet object from inherited base classes: BaseArch with example: obj = RetinaNet(backbone, neck, head)