how to add two numbers and pass the result to the next page in tkinter?

[deanhystad]

It is not good user interface design to have controls in one "page" change displays in a second "page". It is not an absolute, but should give you pause. If you don't immediately see the results of your actions, how do you know that you performed the action correctly? For your example I would put a button in frame 2 that draws a dialog to enter values for first_no and second_no which are applied when you press the "Ok" button in the dialog, or ignored if you press the "Cancel" button.

I cannot tell you what is a good design for your application (I don't know what you are trying to achieve), but I can say you should be spending most of your programming time thinking about the user experience and relatively little time writing code.