I want to pass data between a Python and a C# application in Windows (I want the channel to be bi-directional)
In fact I wanna pass a struct containing data about a network packet that I've captured with C# (SharpPcap) to the Python app and then send back a modified packet to the C# program.
What do you propose ? (I rather it be a fast method)
My searches so far revealed that I can use these technologies, but I don't know which:

JSON-RPC 
Use WCF (run the project
under IronPython using Ironclad)
WCF (use Python for .NET)
Use JSON-RPC because the experience that you gain will have more practical use. JSON is widely used in web applications written in all of the dozen or so most popular languages.
IPC between Python and C#