Maybe my impression has been false this whole time, but the Python interactive interpreter seems to be very similar to the IDLE shell window. My question is, "Why not make them even more so?" Having IDLE react to sys.ps1 and sys.ps2 opens up the shell to similar use cases as having them defined in the interactive interpreter. My suggestion is not to have them added as text as is usual in a terminal window but to print the values of ps1 and ps2 in the proposed ShellIO subclass. That would make label customization possible in a way that is already documented and standard.