def metadata2fname(dataset, pattern='{author}_{title}'):
    """Construct a filename from a metadata set and a pattern.
    
    Args:
        dataset (dict-like): A metadata set, referenced keys subscriptable.
        pattern (str), optional: a general pattern for the desired filename.
            Data keys between braces. Default to "{author}_{title}". 

    Returns:
        A string.
    """
    return pattern.format_map(dataset)
