Re: [Pyobjc-dev] class vs. instance attributes for IBOutlets

[Will L. <le...@gm...>]

Joe,

In order to access the class variable, you'd need to be accessing  
ClassNa property me.instead of 'self.property'. I this this brief  
console session help clarify the difference:

 >>> class Person(object):
...     name = "Tim"
...     age = 25
...
 >>> x = Person()
 >>> x
<__main__.Person object at 0x80870>
 >>> x.name
'Tim'
 >>> x.name = "Will"
 >>> x
<__main__.Person object at 0x80870>
 >>> x.name
'Will'
 >>> Person.name
'Tim'

``x`` starts out with the class instance for ``name``, but once you  
attempt to modify it via ``x.name`` it masks the class property with  
an instance property. This means that you can safely create multiple  
instances of one class that appear to modify class variables without  
causing any trouble. (To actually modify the class property, you'd  
need to do ``Person.x = 'Jack'``.)

I'm curious if InterfaceBuilder can actually detect IBOutlets which  
are initialized inside the __init__ method (not sure), if not, that  
might explain why we've adopted a slightly less Pythonic approach.  
Personally, I'd continue declaring properties as class properties  
until you run into a situation where doing so is strongly undesirable.  
In the long run, it's mostly a stylistic element.

-Will


On Oct 12, 2008, at 10:12 AM, Joe Strout wrote:

> I'm re-learning Python, and learning Cocoa and PyObjC all at the same
> time.  So maybe this is silly question:
>
> The examples I've seen have the IBOutlets (and often data too) defined
> at the class level, like so:
>
> class ToDoListAppDelegate(NSObject):
>     toDoTableView = objc.IBOutlet()
>     newItemField = objc.IBOutlet()
>     toDoList = []
>
>
> But it occurred to me last night that this would be a problem in an
> NSObject class that might have more than one instance -- wouldn't
> apply to the app delegate, of course, but it could apply to a window
> controller.  So I moved the toDoList (which is a mutable type) to the
> init function.  Then, on a lark, I found I could move the IBOutlets
> there too, so it looks like this:
>
> class ToDoListAppDelegate(NSObject):
>     def init(self):
>         NSLog(u"init")
>         self.toDoTableView = objc.IBOutlet()
>         self.newItemField = objc.IBOutlet()
>         self = super(ToDoListAppDelegate, self).init()
>         if self is not None: self.toDoList = []
>         return self
>
> So here's my question: is this necessary for IBOutlets (in a non-
> singleton class of course)?  Or is it not necessary, perhaps because
> this is an immutable type?  And what's the standard best practice for
> these things?
>
> Thanks,
> - Joe
>
>
>
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