While not sure of the behavior you are trying to achieve, XML-RPC comes to mind. But it's based on HTTP protocol in which the client puts request to the server which has to respond. The server cannot initiate interactions. XML-RPC is both widely avalaible, and very easy to implement.
NOTE: in order for the server to raise events in the client, the client needs only raise periodically a *need-anything-from-me* type of request which permits the server to return its request in response to the client. Naturally this solution makes superfluous calls takes some bandwidth, so it might not be appropriate in every circumstance. -- http://mail.python.org/mailman/listinfo/python-list
