ReferenceError: weakly-referenced object no longer exists

[buran]

You don't show how you call your functions, but I assume you call search_book() in order to display the GUI.
You declare cur as global but actually it does not exists in the global scope. Once it complete the execution of the search_book, there are no references to cur and it is destroyed.

So, why do you create cur in search_book in the first place. Why not create it in submit() where it is actually needed and used.
Ideally you should refactor your spaghetti code and not use globals at all. As you see it's terrible to debug problem in such code.

The other "solution" is to initialize cur in the global namespace, e.g. cur = None at the top, after the imports.

As a side note - you use GUI, but print result in stdout??? Not to mention mixing pyautogui and tkinter???