How to write an API for a Python application?

[jmdeschamps at gmail.com]

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.