docs: def update_flagfile(flags_path, new_threshold):
      """Updates the flagfile at `flags_path`, changing the value for
      `resign_threshold` to `new_threshold`
      """
      if abs(new_threshold) > 1:
          raise ValueError("Invalid new percentile for resign threshold")
      with tf.gfile.GFile(flags_path) as f:
          lines = f.read()
      if new_threshold > 0:
          new_threshold *= -1
      if not RESIGN_FLAG_REGEX.search(lines):
          print("Resign threshold flag not found in flagfile {}!  Aborting.".format(flags_path))
          sys.exit(1)
      old_threshold = RESIGN_FLAG_REGEX.search(lines).groups(1)
      lines = re.sub(RESIGN_FLAG_REGEX, "--resign_threshold={:.3f}".format(new_threshold), lines)
  
      if abs(float(old_threshold[0]) - new_threshold) < 0.001:
          print("Not updating percentiles; {} ~= {:.3f}".format(
                  old_threshold[0], new_threshold), flush=True)
      else:
          print("Updated percentile from {} to {:.3f}".format(
                  old_threshold[0], new_threshold), flush=True)
          with tf.gfile.GFile(flags_path, 'w') as f:
              f.write(lines)