def METHOD_NAME(cls, classobj, methodname, filetype):
    def inner_wrapper(wrapped_func):
        key = (classobj, methodname, filetype)
        if key in cls.registry:
            raise ValueError(f'{methodname} for {filetype} is already '
                             f'registered for {classobj.__name__}')
        cls.registry[key] = wrapped_func
        return wrapped_func
    return inner_wrapper