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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_handler_set(cls, request, fail_enum, header_proto=None):
 """Goes through the list of ClientSortControls and returns a list of unique _ValueHandlers. Maintains order, but drops ClientSortControls that have already appeared to help prevent spamming. """

        added = set()
        handlers = []

        for controls in request.sorting:
            control_bytes = controls.SerializeToString()
            if control_bytes not in added:
                added.add(control_bytes)
                handlers.append(
                    cls._ValueHandler(controls, fail_enum, header_proto))

        return handlers