def read_in_github_token_list(file="tokens.txt"):
    """If a tokens file exists, extract tokens line by line.

    This functionality enables reading in multiple GitHub personal
    access tokens so that a user can use the GitHub API more than
    if he or she had only one token.

    Args:
        file - a txt document containing one token per line

    Returns:
        tokens - a list of tokens
    """
    tokens = []
    try:
        with open(file, "r") as token_file:
            for token in token_file:
                # remove whitespace such as returns from token string
                tokens.append(token.strip())
    except FileNotFoundError:
        pass

    return tokens