main window in tkinter app

[William Gill]

That does it!, thanks.

Thinking about it, when I created a derived class with an  __init__ 
method, I  overrode the base class's init.  It should have been 
intuitive that I needed to explicitly call baseclass.__init(self), it 
wasn't.  It might have hit me if the fault was related to someting in 
baseclass.__init() not taking place, but the recursion loop didn't give 
me a clue.  Any idea why failing to init the base class caused the loop?


Bill


Christopher Subich wrote:
> 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.