> So it's impossible to reliably save and restore signal handlers through 
> python when they can also be changed outside the python interpreter.

signal.getsignal() or signal.signal() return the current/previous handler as a Python function. How could it return a reference to a native (i.e. C) signal handler?
While we could in theory return it as a magic cookie (i.e. the handler's address as returned by sigaction/signal) that can just be passed back to signal.signal(), it would be a bad idea: if the user passes an invalid address, the process will crash when the signal is received.