[Tutor] Broblem with exiting a Tkinter app

[Mark Kels]

Hi all ,
I got 2 questions for you guys.

The fist question:
I wrote small Tkinter app while laerning about the Radiobutton widget,
and I added a "Quit" button, like this:
bb=Button(root, text="Quit", fg="BLUE", command=root.quit).pack()
When I pressed the button the app crashed and I got an error message (
program is not responding ) from windows.
I tried to add a frame to the program and then exit the frame, like this:
bb=Button(f, text="Quit", fg="BLUE", command=f.quit).pack()
But the result is the same...

Here is the full source code of the app:
from Tkinter import *
import sys
root=Tk()
f=Frame(root)
text=Label(root, text="how old are you?").pack()
v = IntVar(root)
Radiobutton(f, text="less than 13", variable=v, value=1).pack(side=LEFT)
Radiobutton(f, text="13-20", variable=v, value=2).pack(side=LEFT)
Radiobutton(f, text="20-40", variable=v, value=3).pack(side=LEFT)
Radiobutton(f, text="40+", variable=v, value=4).pack(side=LEFT)
bb=Button(f, text="Quit", fg="BLUE", command=f.quit).pack()
f.pack()
root.mainloop()

The second question:
I dont understand how to get the input fron the radio buttons...
It doesnt returns any value, so how can the app know what the user chose?

Thanks!!