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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 _find_controller(self, class_):
 """Find first controller that matches given request class. Order is specified by the keys of ``SpaceTrackClient.request_controllers`` (:class:`~collections.OrderedDict`) """

        for controller, classes in self.request_controllers.items():
            if class_ in classes:
                return controller
        else:
            raise ValueError('Unknown request class {!r}'.format(class_))