xxv observer concurrency available schedulers online resources exercises rxpy operators introduction reactive programming operators piping operators creational operators transformational operators combinatorial operators filtering operators mathematical operators chaining operators online resources exercises part ix network programming introduction to sockets and web services introduction sockets web services addressing services localhost port numbers ipv versus ipv sockets and web services in python online resources sockets in python introduction socket to socket communication setting up connection an example client server application the system structure implementing the server application socket types and domains implementing the client application the socketserver module http server online resources exercises