you can use a command to call a method and set the value. Please refer attached code.
def sel():
selection = "You selected the option " + str(var.get())
label.config(text = selection)
root = Tk()
frame = Frame(root)
frame.pack()
labelframe = LabelFrame(frame, text="This is a LabelFrame")
labelframe.pack(fill="both", expand="yes")
var = IntVar()
R1 = Radiobutton(labelframe, text="Option 1", variable=var, value=1,
command=sel)
R1.pack( anchor = W )
R2 = Radiobutton(labelframe, text="Option 2", variable=var, value=2,
command=sel)
R2.pack( anchor = W )
R3 = Radiobutton(labelframe, text="Option 3", variable=var, value=3,
command=sel)
R3.pack( anchor = W)
label = Label(labelframe)
label.pack()