A python program opens a new process of the C++ program and is reading the processes stdout.
No problem so far. 
But is it possible to have multiple streams like this for communication? I can get two if I misuse stderr too, but not more. Easy way to hack this would be using temporary files. Is there something more elegant that does not need a detour to the filesystem?
PS: *nix specific solutions are welcome too
assuming windows machine.
you could try using the clipboard for exchanging information between python processes and C++.
assign some unique process id followed by your information and write it to clipboard on python side.....now just parse the string on C++ side.
its akin to using temporary files but all done in memory..... but the drawback being you cannot use clipboard for any other application.
hope it helps
C++ to python communication. Multiple io streams?