two applications exchange data using some file. for example one application creates file "c:\data.dat", writes some data into it, then the second application opens it, reads it, and can edit it, and so on ...
that solution seems quite awkward to me, because there isn't any way to "notify" the second application, and you would have to synchronize the writing/reading mechanism very exactly.
I'not so experienced with sockets in python, so I won't post any code ... but just theoretically:
sockets are used to communicate over tcp/ip, but they can be used locally. one app creates tcp/udp socket on some port, and the second creates client socket and connects to the server. and the data are flowing
maybe there are some extras in Symbian, I don't know. I mean something like windows messaging, windows' memory file mapping, or linux signals.