# In February 1998, we published an introduction, "Getting
#     started with Python" <URL:
#     http://www.sunworld.com/swol-02-1998/swol-02-python.html >,
#     which included an earlier form of this calc.py.  That
#     version doesn't work properly with Python2.0.  This
#     one does, slightly simplifies the text, and also 
#     brings the window up with focus in the entry widget,
#     where it belongs.

from Tkinter import *

def evaluate():
        label['text'] = "Result:  " + str(eval(expression.get()))

frame = Frame(None)

entry = Entry(frame)
entry['textvariable'] = expression = StringVar()
entry.bind("<Return>", lambda event: evaluate())

label = Label(frame)              

button = Button(frame, text = "Submit", command = evaluate)

frame.pack()
entry.pack()
label.pack()
button.pack()

entry.focus_set()
frame.mainloop()