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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 set_shell(self, svc_ref):
 """ Binds the given shell service. :param svc_ref: A service reference """

        if svc_ref is None:
            return

        with self._lock:
            # Get the service
            self._shell_ref = svc_ref
            self._shell = self._context.get_service(self._shell_ref)

            # Set the readline completer
            if readline is not None:
                readline.set_completer(self.readline_completer)

            # Set the flag
            self._shell_event.set()