def count_csv_files(files_string):
    """Count number of DataStream CSV files in census tract

    Parses a string of CSV file paths to determine how many
    individual files there are.

    Args:
        files_string (string): single string of file paths separated by
        commas

    Returns:
        counts (int): number of CSV files
    """
    new_files_string = str(files_string)
    if new_files_string == "nan":
        return 0
    return new_files_string.count(",") + 1