I am trying to write a cross-platform python program that would run in the background, monitor all keyboard events and when it sees some specific shortcuts, it generates one
As the guy that wrote the original pykeylogger linux port, I can say there isn't really a cross platform one. Essentially I rewrote the pyhook API for keyboard events to capture from the xserver itself, using the record extension. Of course, this assumes the record extension is there, loaded into the x server.
From there, it's essentially just detecting if you're on windows, or linux, and then loading the correct module for the OS. Everything else should be identical.
Take a look at the pykeylogger source, in pyxhook.py for the class and implimentation. Otherwise, just load that module, or pyhook instead, depending on OS.