Python Tkinter Menu Command Not Working

Question

I am trying to execute the following code in Python 2.6.5. What I want to do is show a main window with an 'Applications' menu. I want the menu to have a series of commands which should correspond to the keys of the Apps dictionary. When I click the command, I would like the default web browser to open and navigate to the url in the Apps dictionary for that particular key. Instead, when I execute the code the browser is opening to the first url in the Apps dictionary without any clicking. Help please!

from Tkinter import *
import webbrowser

#Real links are to pages on Intranet.
Apps={
     'Google':'http://www.google.com/',
     'Yahoo':'http://www.yahoo.com/'
     }

def openApp(appURL):
     webbrowser.open(appURL, new=1, autoraise=1)
     return None

root=Tk()
menubar=Menu(root)
root.config(menu=menubar)
appsMenu=Menu(menubar)
for app in Apps:
     appsMenu.add_command(label=app, command=openApp(Apps[app]))
menubar.add_cascade(label='Apps', menu=appsMenu)
root.mainloop()

Answer 1

 appsMenu.add_command(label=app, command=openApp(Apps[app]))

Command parameters that call functions need to be wrapped in a lambda , to prevent them from being called right away. Additionally, commands bound within a for loop need the looping variable as a default argument, in order for it to bind the right value each time.

 appsMenu.add_command(label=app, command=lambda app=app: openApp(Apps[app]))