def get_vocab_file_substring(include_retweets, max_ngram_len):
    """Get the substring with parameters for the saved data filename.

    >>> get_vocab_file_substring(False, 2)
    'vocab-retweets-False-ngrams-1-to-2'
    """
    return "-".join(
        [
            "vocab",
            "retweets",
            str(include_retweets),
            "ngrams",
            str(1),
            "to",
            str(max_ngram_len),
        ]
    )