[Tutor] apply() after class?

[Alan Gauld]

"Wayne Watson" <sierra_mtnview at sbcglobal.net> wrote 

> Ah, another function without a link to a use. body, as in :
> 
> class SetDecoderDialog(tkSimpleDialog.Dialog):
>    def body(self,master):
>        self.title("Set Video Decoder Register")
> 
>        Label(master, text='Register:').grid(row=0, sticky=W)
>        Label(master, text='New Value:').grid(row=1, sticky=W)
> 
>        self.reg = Entry(master, width=10)
>        self.val = Entry(master, width=10)
> 
>        self.reg.grid(row=0, column=1, sticky=W)
>        self.val.grid(row=1, column=1, sticky=W)
> 
>        return self.reg
> 
>    def apply(self):
>        reg = eval(self.reg.get())
>        val = eval(self.val.get())
>        self.gui.SetDecoder( reg, val )
> 
> That's the end of the class. Is there something going on 
> here between body-apply and tkSimpleDialog? 
> Making them available to it?

Yes. This is part of the power of OOP.
If we create an instance of this class it inherits all of the 
methods of simpleDialog. But if one of those methods internally 
calls self.body or self.apply it will  for this instance execute
SetDecoderDialog.body or SetDecoderDialog.apply

This is a form of polymorphism which is commonly used 
in object frameworks.

Now I don't know whether SimpleDialog does do that 
but it is entirely possible. Thus it would not seem like 
anything is calling those two functions but in fact they 
are being called indirectly. (A couple of print statements 
would show whether they were or not!)

HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld