code: def check_files_exist(in_ss_out_names, key, num_partitions):
      for i in range(num_partitions):
          if not os.path.exists(in_ss_out_names[i][key]):
              return False
      return True
  
imports: import argparse
  import math
  import json
  import os
  import sys
  import time
  import gzip
  import glob
  import torch
  import numpy
  import multiprocessing
  from megatron.tokenizer import build_tokenizer
  from megatron.core.datasets import indexed_dataset
label_desc: Use image node_id 3 for calling a global function with example usage: check_files_exist(in_ss_out_names, key, num_partitions) and returns: True, False