code: def parse_anchor(self, anchors, anchor_masks):
      self.anchors = [
          [anchors[i] for i in mask] for mask in anchor_masks
      ]
      self.mask_anchors = []
      anchor_num = len(anchors)
      for masks in anchor_masks:
          self.mask_anchors.append([])
          for mask in masks:
              assert mask < anchor_num, "anchor mask index overflow"
              self.mask_anchors[-1].extend(anchors[mask])
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle import ParamAttr
  from paddle.regularizer import L2Decay
  from ppdet.core.workspace import register
  import math
  import numpy
  from ..initializer import bias_init_with_prob, constant_
  from ..backbones.csp_darknet import BaseConv, DWConv
  from ..losses import IouLoss
  from ppdet.modeling.assigners.simota_assigner import SimOTAAssigner
  from ppdet.modeling.bbox_utils import bbox_overlaps
  from ppdet.modeling.layers import MultiClassNMS
label_desc: Use image node_id 2 for calling the YOLOv3Head obj's underlying member method code with example usage: obj.parse_anchor(anchors, anchor_masks) without return types