docstr: Return `int` of num classes 
docstr_tok: ["Return","`","int","`","of","num","classes"]
code: def n_classes(self):
      """Return `int` of num classes"""
      raise NotImplementedError
  
imports: import os
  import numpy
  import torch.utils.data
  import torchvision.transforms
  import torchvision.datasets
label_desc: Use image node_id 3 for calling the DataProvider obj's underlying member method code with example usage: obj.n_classes() without return types