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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def method(method_class):
 """Decorator to use to mark an API method. When invoking L{Registry.scan} the classes marked with this decorator will be added to the registry. @param method_class: The L{Method} class to register. """


    def callback(scanner, name, method_class):
        if method_class.actions is not None:
            actions = method_class.actions
        else:
            actions = [name]

        if method_class.versions is not None:
            versions = method_class.versions
        else:
            versions = [None]

        for action in actions:
            for version in versions:
                scanner.registry.add(method_class,
                                     action=action,
                                     version=version)

    from venusian import attach
    attach(method_class, callback, category="method")
    return method_class