class_docstr: PglGraphPropPredDataset
docstr: Length of the dataset
  Returns
  -------
  int
      Length of Dataset
docstr_tok: ["Length","of","the","dataset","Returns","--","--","--","-","int","Length","of","Dataset"]
code: def __len__(self):
      """Length of the dataset
      Returns
      -------
      int
          Length of Dataset
      """
      return len(self.graphs)
  
file_path: PGL/legacy/pgl/contrib/ogb/graphproppred/dataset_pgl.py
imports: import pandas
  import shutil, os
  import os.path
  import numpy
  from ogb.utils.url import decide_download, download_url, extract_zip
  from ogb.graphproppred import make_master_file
  from pgl.contrib.ogb.io.read_graph_pgl import read_csv_graph_pgl
label_desc: Use image node_id 5 for calling the PglGraphPropPredDataset obj's underlying member method code with example usage: obj.__len__() and returns: len