Blocking behavior of PyGTK's main loop

My intention was to use pyGTK's main loop to create a function that blocks while it waits for the user's input. The problem I've encountered is best explained in code:

#! /usr/bin/python

import gtk

def test():
    retval = True
    def cb(widget):
        retval = False
        gtk.main_quit()

    window = gtk.Window(gtk.WINDOW_TOPLEVEL)
    button = gtk.Button("Test")
    button.connect("clicked", cb)
    button.show()
    window.add(button)
    window.show()

    gtk.main()
    return retval

if __name__ == "__main__":
    print test() # prints True when the button is clicked

It seems that the exact order of instructions (change value of retval, then exit main loop) isn't being followed here开发者_C百科.

Is there any way around this, or is this just bad design on my part?

This is the dialog pattern. Use a gtk.Dialog. Dialog.run() blocks exactly how you need it to, and returns the dialog's return code.

What is happening is that when python sees foo = bar as the first reference to foo in a function it assumes that it is a local variable. In python3k you can get around this by using the nonlocal keyword. For 2.x you can wrap your retval in a list so that you aren't directly assigning to it.

retval = [True]
def cb(widget):
    retval[0] = False
    gtk.main_quit()
...
return retval[0]

not really an elegant solution, hence the addition of nonlocal in 3.x (PEP)