[Tkinter] Unable to Obtain values from one Tkinter Program into another

[Gribouillis]

You must not call .mainloop() more than once. You could read this tutorial at effbot to create a dialog window. Look at the tkSimpleDialog.py file the key steps are in the dialog class' __init__() method, namely the calls to grab_set(), focus_set(), wait_window(). You may need to adapt this code to python 3 (which is easy).