William Gill wrote:
> O.K. I tried from scratch, and the following snippet produces an
> infinite loop saying:
>
> File "C:\Python24\lib\lib-tk\Tkinter.py", line 1647, in __getattr__
> return getattr(self.tk, attr)
>
> If I comment out the __init__ method, I get the titled window, and print
> out self.var ('1')
>
>
> import os
> from Tkinter import *
>
> class MyApp(Tk):
> var=1
> def __init__(self):
> pass
> def getval(self):
> return self.var
>
>
> app = MyApp()
>
> app.title("An App")
> print app.getval()
> app.mainloop()
You're not calling the parent's __init__ inside your derived class. I
would point out where the Python Tutorial points out that you should do
this, but it's not in the obvious place (Classes: Inheritance).
Python does -not- automagically call parent-class __init__s for derived
classes, you must do that explicitly. Changing the definition of your
class to the following works:
>>> class MyApp(Tk):
var=1
def __init__(self):
Tk.__init__(self)
pass
def getval(self):
return self.var
It works when you comment out __init__ because of a quirk in Python's
name resolution. As you'd logically expect, if you don't define a
function in a derived class but call it (such as instance.method()), it
will call the method from the base class.
You just proved that this works for __init__ methods also. When you
didn't define __init__ for your derived class, MyApp() called
Tk.__init__(), which Does the Right Thing in terms of setting up all the
specific Tkinter-specific members.
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