code: def train_unsharded(self):
      return iter(self._train_unsharded)
  
imports: import csv
  import logging
  import sys
  import threading
  from typing import Dict, List, Optional, Type
  from pytext.utils.path import get_absolute_path
  from .data_source import generator_property, RootDataSource, SafeFileWrapper, ShardedDataSource
  from .session import SessionDataSource
label_desc: Use image node_id 3 for calling the BlockShardedTSVDataSource obj's underlying member method code with example usage: obj.train_unsharded() and returns: iter