main window in tkinter app

Christopher Subich spam.csubich+block at block.subich.spam.com
Wed Jul 20 19:00:09 CEST 2005


William Gill wrote:
> 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?

You never pasted the first part of the traceback:

   File "<pyshell#204>", line 1, in -toplevel-
     app.title('frob')
   File "C:\Python24\Lib\lib-tk\Tkinter.py", line 1531, in wm_title
     return self.tk.call('wm', 'title', self._w, string)
   File "C:\Python24\Lib\lib-tk\Tkinter.py", line 1654, in __getattr__
     return getattr(self.tk, attr)
   File "C:\Python24\Lib\lib-tk\Tkinter.py", line 1654, in __getattr__
     return getattr(self.tk, attr)

When you didn't call Tk.__init__(self), self.tk was never initialized. 
Further, it's obvious from the traceback that Tk implements a 
__getattr__ method; from the python docs:

__getattr__(self,name): Called when an attribute lookup has not found 
the attribute in the usual places

Since self.tk doesn't exist, __getattr__(self,tk) was called.  Without 
looking at the TKinter source code, we can surmise that there's a 
default behavior of "if self doesn't have it, return the relevant 
attribute from within self.tk."  The problem, of course, arises when 
self.tk doesn't exist -- this causes the self.tk reference to call 
self.__getattr__('tk'), which is recursive.

The infinite recursion, then, is a mild bug in TKinter that doesn't show 
itself during normal use.  The proper solution should be to replace the 
self.tk call with either self.__dict__['tk'], or to make Tk a new-style 
class and use object.__getattribute__(self,'tk'). (Note: there are 
probably some fine details that I'm missing in this 'solution', so take 
it with a potato-sized grain of salt.  The general principle still 
applies though.)



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