Simple IPC between C++ and Python (cross platform)
zeromq -- and nothing else. encode the messages as strings.
However, If you want to get serialiazation from a library use protobuf it will generate classes for Python and C++. You use the SerializeToString() and ParseFromString() functions on either end, and then pipe the strings via ZeroMq.
Problem solved, as I doubt any other solution is faster, and neither will any other solution be as easy to wire-up and simple to understand.
If want to use specific system primitives for rpc such as named pipes on Windows and Unix Domain Sockets on unix then you should look at Boost::ASIO. However, unless you have (a) a networking background, and (b) a very good understanding of C++, this will be very time consuming