Changing a variable value , by a class (python)

Question

I can't change a value from a class.

This is my problem :

#!/usr/bin/env python

import pygtk
pygtk.require20()
import gtk

class MyApp(object):
    def __init__(self):
        self.pencere = gtk.Window(gtk.WINDOW_TOPLEVEL)
        self.pencere.connect("delete_event", gtk.main_quit)

        self.b_Up = gtk.Button("UP")
        self.b_Down = gtk.Button("DOWN")
        self.b_Up.connect("pressed", self.ToUp)
        self.b_Down.connect("pressed", self.ToDown)

        self.tablo = gtk.Table(2, 1, False)
        self.tablo.attach(self.b_Up , 0, 1, 0,1)
        self.tablo.attach(self.b_Down, 1, 2, 0, 1 )

        self.pencere.add(self.tablo)

        self.pencere.show_all()
        return

    def ToUp(self, penar  ):
        print "==========ClassUp======= \n" , var_a
        print "@ToUP : " , var_a
        ChangeUp()
        print var_a , "\n=========ClassEndUp========"

    def ToDown(self, penar):
        print "==========ClassDown======= \n", var_a
        print "@ToDown : ", var_a
        ChangeDown()
        print var_a , "\n========ClassEndDown========="

    def main(self):
        gtk.main()

def ChangeUp():
    print "Changing Up : ", var_a
    var_a=["90", "91", "92", "93", "94", "95", "96", "97", "98", "99" ]
    print var_a , "\n================="


def ChangeDown():
    print "Changing Down : " , var_a
    var_a=["0", "1", "2", "3", "4", "5", "6", "7", "8", "9" ]
    print var_a , "\n================="


var_a=["30", "31", "32", "33", "34", "35", "36", "37", "38", "39" ]

app = MyApp()
app.main()

i want to change the var_a list value everywhere When i click a button ; i am taking an error message :

==========ClassDown======= 
['30', '31', '32', '33', '34', '35', '36', '37', '38', '39']
@ToDown :  ['30', '31', '32', '33', '34', '35', '36', '37', '38', '39']
Changing Down : 
Traceback (most recent call last):
  File "aa.py", line 35, in ToDown
    ChangeDown()
  File "aa.py", line 48, in ChangeDown
    print "Changing Down : " , var_a
UnboundLocalError: local variable 'var_a' referenced before assignment

i want to change var_a list value by clicking . not only in class , everywhere. i tried using "global" but i cant :( (i took an error message).

How can i solve this problem ?

UnboundLocalError: local variable 'var_a' referenced before assignment

i don't know python well i am beginner. so if u write the code i will be very happy :) thanks a lot !!

var_a=["30", "31", "32", "33", "34", "35", "36", "37", "38", "39" ] — Chedy2149
– Chedy2149, Commented Dec 23, 2012 at 15:28
The best answer is not to use globals. They are a bad idea in general, as they make it much harder to follow the code. — Gareth Latty
– Gareth Latty, Commented Dec 23, 2012 at 15:31

Mark Byers · Accepted Answer · 2012-12-23 15:51:32Z

3

Your method defines a new local variable called var_a that hides the global variable with the same name.

To fix it you can add a global declaration at the beginning of the method:

def ChangeDown():
    global var_a
    print "Changing Down : " , var_a
    var_a=["0", "1", "2", "3", "4", "5", "6", "7", "8", "9" ]
    print var_a , "\n================="

However I would advise you not to use globals if it is at all possible. Consider using an instance variable instead.

edited Dec 23, 2012 at 15:51

answered Dec 23, 2012 at 15:24

Mark Byers

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