For laying out your number buttons you might want to investigate the grid geometry manager rather than using pack. As the name suggests, it allows you to lay buttons out in rows and columns more easily than pack can. You don't have to use one or the other exclusively but can mix them as appropriate. I have found it useful to lay out frames in my main window using pack to get them in the right relationship to each other and then to populate them with the buttons and other widgets I need. You can place buttons using grid in a frame that you have packed.

Cheers,

JohnGG