code: def __getitem__(self, i):
      return self.pq_per_cat[i]
  
imports: from collections import defaultdict
  import numpy
  from paddlepanseg.cvlibs import build_info_dict
  from paddlepanseg.utils import decode_pan_id
  from .evaluator import Evaluator
label_desc: Use image node_id 2 for calling the PQStat obj's underlying member method code with example usage: obj.__getitem__(i) and returns: self