code: def load_annotations(self):
      assert self.data_type == "mcmot"
      self.gt_filename = os.path.join(
          self.data_root,
          "../",
          "sequences",
          "{}.txt".format(self.seq_name),
      )
      if not os.path.exists(self.gt_filename):
          logger.warning(
              "gt_filename '{}' of MCMOTEvaluator is not exist, so the MOTA will be -INF."
          )
  
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
  import pandas
  from .metrics import Metric
  from ppdet.utils.logger import setup_logger
label_desc: Use image node_id 2 for calling the MCMOTEvaluator obj's underlying member method code with example usage: obj.load_annotations() without return types