docs: def subsample():
      """Sample num_positions postions from each game in sgf_dir
  
      Usage:
          python3 sharp_positions.py subsample --num_positions 10 --sgf_dir data/s
  
      NOTE(sethtroisi): see link for a script to truncate SGFs at move number
          https://github.com/sethtroisi/go-scripts
      """
  
      sgf_files = oneoff_utils.find_and_filter_sgf_files(
          FLAGS.sgf_dir, None, None)
  
      with open(FLAG.collection, 'w') as collection:
          fails = 0
          for path in tqdm(sorted(sgf_files)):
              try:
                  positions, moves, results = oneoff_utils.parse_sgf(path)
              except KeyboardInterrupt:
                  raise
              except Exception as e:
                  fails += 1
                  print("Fail {}, while parsing {}: {}".format(fails, path, e))
                  continue
  
              moves = len(positions)
              indexes = random.sample(range(10, moves), FLAGS.num_positions)
              for index in sorted(indexes):
                  collection.write('{}, {}\n'.format(path, index))