code: def __len__(self):
      return self.num_samples
  
file_path: insightface/detection/scrfd/mmdet/datasets/samplers/group_sampler.py
imports: from __future__ import division
  import math
  import numpy
  import torch
  from mmcv.runner import get_dist_info
  from torch.utils.data import Sampler
label_desc: Use image node_id 3 for calling the GroupSampler obj's underlying member method code with example usage: obj.__len__() and returns: self