def format_number(number, format):
    """Format `number` according the given `format` (:class:`NumberFormat`)"""
    if format == NumberFormat.NUMBER:
        return str(number)
    elif format == NumberFormat.LOWERCASE_CHARACTER:
        string = ''
        while number > 0:
            number, ordinal = divmod(number, 26)
            if ordinal == 0:
                ordinal = 26
                number -= 1
            string = chr(ord('a') - 1 + ordinal) + string
        return string
    elif format == NumberFormat.UPPERCASE_CHARACTER:
        return format_number(number, 'lowercase character').upper()
    elif format == NumberFormat.LOWERCASE_ROMAN:
        return romanize(number).lower()
    elif format == NumberFormat.UPPERCASE_ROMAN:
        return romanize(number)
    elif format == NumberFormat.SYMBOL:
        return symbolize(number)
    elif format == NumberFormat.NONE:
        return ''
    else:
        raise ValueError("Unknown number format '{}'".format(format))
Format `number` according the given `format` (:class:`NumberFormat`)