What's wrong with this code? (UnboundLocalError: local variable referenced before assignment)

[John Gordon]

In <b3d3518a-f24a-4c32-a41a-b99145753528 at googlegroups.com> pablobarhamalzas at gmail.com writes:

> isWhite = True
>         
> def change(event):
>     if event.x > x1 and event.x < x2 and event.y > y1 and event.y < y2:
>         if isWhite:
>             w.itemconfig(rect, fill="blue")
>             isWhite = False
>         else:
>             w.itemconfig(rect, fill="white")   
>             isWhite = True
>                               
> w.bind("<Button-1>", change)
>       
> root.mainloop()  

> The problem occurs when clicking on the white square. The following error
> appears:
> "if isWhite:
> UnboundLocalError: local variable 'isWhite' referenced before assignment"

> However, the isWhite variable is clearly defined at "True" a few lines
> before.

Since you're new to programming, this might be a bit tricky to explain,
but I'll do my best. :-)

The problem is that change() isn't being executed here; instead it's being
executed from within root.mainloop(), whenever the user presses button-1.

And within root.mainloop(), there is no variable called isWhite.

-- 
John Gordon                   A is for Amy, who fell down the stairs
gordon at panix.com              B is for Basil, assaulted by bears
                                -- Edward Gorey, "The Gashlycrumb Tinies"