class_docstr: 自定义数据集
class_docstr_tok: ["\u81ea\u5b9a\u4e49\u6570\u636e\u96c6"]
code: def __len__(self):
      return self.total_num
  
file_path: deep-learning-for-image-processing/pytorch_classification/mini_imagenet/my_dataset.py
imports: import os
  import json
  from PIL import Image
  import pandas
  import torch
  from torch.utils.data import Dataset
label_desc: Use image node_id 2 for calling the MyDataSet obj's underlying member method code with example usage: obj.__len__() and returns: self