For C++ it may be easier to use XRC.
For Python it does not add value and not support all features. It will prevent you from stepping through with the debugger or add elements on the debugger console.
If you want to do it the hard way, create the GUI in code. If you want to make your life easier, use wxGlade as GUI builder and work through the tutorial. This will get you started with wxPython.
Remember to download and run also the wxPython demo.
Regards,
Dietmar