why function throws an error?

[נתי שטרן]

        def add_route(self, route):
        #    """ Add a route object, but do not change the :data:`Route.app`
        #        attribute."""
            self.routes.append(route)
            self.router.add(route.rule, route.method, route, name=route.name
)
        #    if DEBUG: route.prepare()
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