<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def read_vocab(args, column_name):
 """Reads a vocab file if it exists. Args: args: command line flags column_name: name of column to that has a vocab file. Returns: List of vocab words or [] if the vocab file is not found. """

  vocab_path = os.path.join(args.analysis,
                            feature_transforms.VOCAB_ANALYSIS_FILE % column_name)

  if not file_io.file_exists(vocab_path):
    return []

  vocab, _ = feature_transforms.read_vocab_file(vocab_path)
  return vocab