[Tutor] OOP clarification needed

[Jim Byrnes]

Steve Willoughby wrote:
> On Tue, Jun 01, 2010 at 03:19:17PM -0500, Jim Byrnes wrote:
>> def viewer(imgdir, kind=Toplevel, cols=None):
>>      win = kind()
>>
>> What is the relationship between kind=Toplevel in the first line and
>> win=kind() further down.  Isn't "kind" a variable and "kind()" a method?
>
> kind is a variable.  Specifically, the second parameter passed to the viewer()
> function defined here.
>
> By saying kind() here, you are invoking it on the assumption that kind's
> value is a reference to some kind of callable object.  So in theory you
> could pass a function as the "kind" parameter of viewer() and that function
> would get called, and its return value stored in "win".
>
> In this case, though, the intent is for "kind" to refer to an object class
> (the kind of widget this viewer is contained in or whatever).  Recalling that
> object classes are themselves callable objects (specifically, calling them
> is how you construct new instances of a class), "win" will end up referring
> to a newly-constructed instance of whatever object class was passed as "kind".
> If no "kind" parameter was given, it will default to tk.Toplevel.
>

Thanks for the explanation.  I didn't understand how (or why) "kind" 
could change to "kind()". Sometimes I can manage to trip myself up over 
the silliest things.

Regards,  Jim