questions about Exceptions?

[skanemupp at yahoo.se]

here is the whole code:

from __future__ import division
import Tkinter
from Tkinter import *

mygui = Tkinter.Tk()
mygui.title("Calculator")

w = Label(mygui, text="Answer: ")
w.place(relx=0.15, rely=0.1, anchor=CENTER)

nbr = ""

def Disp(nstr):
    global nbr
    nbr=nbr+nstr
    print "You need to seek help!",nbr

def Calc():
    global nbr
    try:
        print eval(nbr)
        #a = Label(mygui, text=eval(nbr))
        #a.place(relx=0.4, rely=0.1, anchor=CENTER)
    except:
        print "Not computable"
    nbr = ""

def Erase():
    global nbr
    nbr = ""


b = Button(mygui, text="1",command=lambda n='1':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.2, anchor=CENTER)
b = Button(mygui, text="2",command=lambda n='2':Disp(n), width=2,
height=1)
b.place(relx=0.2, rely=0.2, anchor=CENTER)
b = Button(mygui, text="3",command=lambda n='3':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.2, anchor=CENTER)
b = Button(mygui, text="+",command=lambda n='+':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.2, anchor=CENTER)
b = Button(mygui, text="4",command=lambda n='4':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.3, anchor=CENTER)
b = Button(mygui, text="5",command=lambda n='5':Disp(n), width=2,
height=1)
b.place(relx=0.2, rely=0.3, anchor=CENTER)
b = Button(mygui, text="6",command=lambda n='6':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.3, anchor=CENTER)
b = Button(mygui, text="-",command=lambda n='-':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.3, anchor=CENTER)
b = Button(mygui, text="7",command=lambda n='7':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.4, anchor=CENTER)
b = Button(mygui, text="8",command=lambda n='8':Disp(n), width=2,
height=1)
b.place(relx=0.2, rely=0.4, anchor=CENTER)
b = Button(mygui, text="9",command=lambda n='9':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.4, anchor=CENTER)
b = Button(mygui, text="*",command=lambda n='*':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.4, anchor=CENTER)
b = Button(mygui, text="0",command=lambda n='0':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.5, anchor=CENTER)
b = Button(mygui, text="C",command=Erase, width=2, height=1)
b.place(relx=0.2, rely=0.5, anchor=CENTER)
b = Button(mygui, text="^.5",command=lambda n='**.5':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.5, anchor=CENTER)
b = Button(mygui, text="/",command=lambda n='/':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.5, anchor=CENTER)
b = Button(mygui, text="=",command=Calc, width=2, height=1)
b.place(relx=0.2, rely=0.7, anchor=CENTER)

mygui.mainloop()