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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 get_content_models(self):
 """ Return all Page subclasses that are admin registered, ordered based on the ``ADD_PAGE_ORDER`` setting. """

        models = super(PageAdmin, self).get_content_models()

        order = [name.lower() for name in settings.ADD_PAGE_ORDER]

        def sort_key(page):
            name = "%s.%s" % (page._meta.app_label, page._meta.object_name)
            unordered = len(order)
            try:
                return (order.index(name.lower()), "")
            except ValueError:
                return (unordered, page.meta_verbose_name)
        return sorted(models, key=sort_key)