def check_format(format):
    if (format is None):
        format = 'SVG'
    fmt = format.lower()
    supported_formats = ['svg', 'ascii', 'unicode']
    if (fmt not in supported_formats):
        raise ValueError("Unknown format '{}'. Supported formats are {}".format(format, supported_formats))
    return fmt
def check_format(format):
    if (format is None):
        format = 'SVG'
    fmt = format.lower()
    supported_formats = ['svg', 'ascii', 'unicode']
    if (fmt not in supported_formats):
        raise ValueError("Unknown format '{}'. Supported formats are {}".format(format, supported_formats))
    return fmt