class_docstr: Download data from https://rajpurkar.github.io/SQuAD-explorer/
  Will return tuples of (doc, question, answer, answer_start, has_answer)
class_docstr_tok: ["Download","data","from","https",":","\/\/rajpurkar.github.io\/SQuAD-explorer\/","Will","return","tuples","of","(","doc",",","question",",","answer",",","answer_start",",","has_answer",")"]
code: def train(self):
      return self.process_file(self.train_filename)
  
imports: import json
  import math
  from random import choice
  from typing import List, Optional
  from pytext.data.sources.data_source import DataSource, generator_property, JSONString, SafeFileWrapper
  from pytext.data.sources.tsv import TSV
  from pytext.utils.file_io import PathManager
  from pytext.utils.path import get_absolute_path
label_desc: Use image node_id 6 for calling the SquadDataSource obj's underlying member method code with example usage: obj.train() and returns: self