Question

I have two files that I am trying to work with. menu.py has the menus that program.py imports.

menu.py:

import cmd,sys

user = 'no one'

class loginMenu(cmd.Cmd):
    def postloop(self):
        user = 'lilith'
        return user
    intro="""login menu"""
    def do_smtoggle(self,person):
        return True

    def do_quit(self,person):
        sys.exit()

class storeMenu(cmd.Cmd):
    intro="""store menu"""
    def do_whoami(self,person):
        print 'storemenu ' + user
    def do_quit(self,person):
        quit = True
        return quit

program.py:

from menu import *
import cmd,sys

lm = loginMenu()
sm = storeMenu()

while True:
    lm.cmdloop()
    print user
    sm.cmdloop()

I expect that when program.py gets to print user it will print lilith but instead it prints no one. Why is this? postloop() is defined in the docs as a method that executes when cmdloop() is about to return so I thought it would return the value of user as lilith and then lilith would be printed but it just prints no one.

edit: It has been recommended that I not use globals. I am reading this to find out why.

Answer 1

That’s because the assignment to user here:

def postloop(self):
    user = 'lilith'
    return user

is acting on a local instance of the var. To affect the global var user, you would need to add a:

global user

to the top of that function. Though I wouldn’t recommend it, as there are usually better ways to do things than to use globals.

One note about globals and python. While you can’t assign a value to a global var without the global keyword, you can read global (and other non-local) scopes, without it. This allows you to make closures.