code: def load_annotations(self):
      assert self.data_type == "mot"
      gt_filename = os.path.join(
          self.data_root, self.seq_name, "gt", "gt.txt"
      )
      if not os.path.exists(gt_filename):
          logger.warning(
              "gt_filename '{}' of MOTEvaluator is not exist, so the MOTA will be -INF."
          )
      self.gt_frame_dict = read_mot_results(gt_filename, is_gt=True)
      self.gt_ignore_frame_dict = read_mot_results(
          gt_filename, is_ignore=True
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import copy
  import sys
  import math
  from collections import defaultdict
  import numpy
  from ppdet.modeling.bbox_utils import bbox_iou_np_expand
  from .map_utils import ap_per_class
  from .metrics import Metric
  from .munkres import Munkres
  from ppdet.utils.logger import setup_logger
label_desc: Use image node_id 2 for calling the MOTEvaluator obj's underlying member method code with example usage: obj.load_annotations() without return types