class_docstr: step 1：paddle.io.Dataset
docstr: step 4：implement __len__
docstr_tok: ["step","4\uff1aimplement","__len__"]
code: def __len__(self):
      """
      step 4：implement __len__
      """
      return len(self.data)
  
file_path: PaddleHub/modules/image/classification/SpinalNet_Gemstones/gem_dataset.py
imports: import paddle
  import numpy
  from typing import Callable
  from code.config import config_parameters
label_desc: Use image node_id 3 for calling the GemStones obj's underlying member method code with example usage: obj.__len__() and returns: len