class_docstr: 可以被输入到分类模型中的普通数据集
code: def __len__(self):
      return self.num_of_data
  
imports: from functools import reduce
  from numpy import dtype
  from fastNLP.envs.imports import _NEED_IMPORT_TORCH
label_desc: Use image node_id 2 for calling the TorchNormalXYDataset obj's underlying member method code with example usage: obj.__len__() and returns: self