tween the check for the license' existence in the requesthandler cars dictionary and adding the new car to the dictionary def shutdown(self*ignore)self server shutdown(raise finish(if the action is to shut down we call the server' shutdown(method--this will stop it from accepting any further requestsalthough it will continue running while it is still servicing any existing requests we then raise custom exception to notify the handler(that we are finished--this causes the handler(to return without sending any reply to the client summary ||this showed that creating network clients and servers can be quite straightforward in python thanks to the standard library' networking modulesand the struct and pickle modules in the first section we developed client program and gave it single functionhandle_request()to send and receive arbitrary picklable data to and from server using generic data format of "length plus picklein the second section we saw how to create server subclass using the classes from the socketserver module and how to implement request handler class to service the server' client requests here the heart of the network interaction was confined to single methodhandle()that can receive and send arbitrary picklable data from and to clients the socket and socketserver modules and many other modules in the standard librarysuch as asyncoreasynchatand sslprovide far more functionality than we have used here but if the networking facilities provided by the standard library are not sufficientor are not high-level enoughit is worth looking at the third-party twisted networking framework (www twistedmatrix comas possible alternative exercises ||the exercises involve modifying the client and server programs covered in this the modifications don' involve lot of typingbut will need little bit of care to get right copy car_registration_server py and car_registration py and modify them so that they exchange data using protocol versioned at the network level this could be donefor exampleby passing two integers in the struct (lengthprotocol versioninstead of one