Stop/break the VRP program if no solution is found

[Westlife1002]

I have an GUI for the VRP model, developed based on tkinter.
When clicking the "run" button and if there is "no solution", it gets stuck and no way to exit and to print ("no solution"). I guess it's the VRP programming still running. Is there any way to stop the VRP part of the program if no solution is found, and also print ("no solution")

my lastest codes is here:
https://gist.github.com/Westlife1002/03f5f2a1b03841a81221623bce63951e