def METHOD_NAME(cls, classdict, bases, docval_args, spec):
    """Convert classdict['__columns__'] to tuple.
    :param classdict: The class dictionary.
    :param bases: The list of base classes.
    :param docval_args: The dict of docval arguments.
    :param spec: The spec for the container class to generate.
    """
    # convert classdict['__columns__'] from list to tuple if present
    columns = classdict.get('__columns__')
    if columns is not None:
        classdict['__columns__'] = tuple(columns)