class_docstr: Used in RetinaNet proposed in paper https://arxiv.org/pdf/1708.02002.pdf
      
class_docstr_tok: ["Used","in","RetinaNet","proposed","in","paper","https",":","\/\/arxiv.org\/pdf\/1708.02002.pdf"]
code: def get_bboxes_single(
      self,
      anchors,
      cls_scores_list,
      bbox_preds_list,
      im_shape,
      scale_factor,
      rescale=True,
  ):
      assert len(cls_scores_list) == len(bbox_preds_list)
      mlvl_bboxes = []
      mlvl_scores = []
      for anchor, cls_score, bbox_pred in zip(
          anchors, cls_scores_list, bbox_preds_list
      ):
          cls_score = cls_score.reshape([-1, self.num_classes])
          bbox_pred = bbox_pred.reshape([-1, 4])
          if (
              self.nms_pre is not None
              and cls_score.shape[0] > self.nms_pre
          ):
              max_score = cls_score.max(axis=1)
              _, topk_inds = max_score.topk(self.nms_pre)
              bbox_pred = bbox_pred.gather(topk_inds)
              anchor = anchor.gather(topk_inds)
              cls_score = cls_score.gather(topk_inds)
          bbox_pred = delta2bbox(
              bbox_pred, anchor, self.weights
          ).squeeze()
          mlvl_bboxes.append(bbox_pred)
          mlvl_scores.append(F.sigmoid(cls_score))
      mlvl_bboxes = paddle.concat(mlvl_bboxes)
      mlvl_bboxes = paddle.squeeze(mlvl_bboxes)
      if rescale:
          mlvl_bboxes = mlvl_bboxes / paddle.concat(
              [scale_factor[::-1], scale_factor[::-1]]
          )
      mlvl_scores = paddle.concat(mlvl_scores)
      mlvl_scores = mlvl_scores.transpose([1, 0])
      return mlvl_bboxes, mlvl_scores
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import math
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle import ParamAttr
  from paddle.nn.initializer import Normal, Constant
  from ppdet.modeling.bbox_utils import bbox2delta, delta2bbox
  from ppdet.modeling.heads.fcos_head import FCOSFeat
  from ppdet.core.workspace import register
label_desc: Use image node_id 4 for calling the RetinaHead obj's underlying member method code with example usage: obj.get_bboxes_single(anchors, cls_scores_list, bbox_preds_list, im_shape, scale_factor, rescale) and returns: mlvl_bboxes,  mlvl_scores