Re: [Pyobjc-dev] another odd problem

[Ronald O. <ous...@ci...>]

On Saturday, 9 August, 2003, at 19:53, Steven D. Arnold wrote:

> Essentially, it seems classes that inherit from Foundation.NSObject do 
> not
> correctly see methods in superclasses before the one that inherited 
> from
> NSObject.  However, note that dir does show the attribute!  Consider 
> the
> following code snippet:
>
>     import Foundation
>     class ListManager:
>         def init( self ):
>             return self
>         def key_for_index( self, index ):
>             print "INDEX = ", index
>
>     class foo( Foundation.NSObject, ListManager ):
>         def init( self ):
>             ListManager.init( self )
>             return self
>
>     i = foo.alloc().init()
>     if 'key_for_index' in dir( i ):
>         present = "is"
>     else:
>         present = "is not"
>
>     print "dir shows that key_for_index %s an attribute of i" % present
>     i.key_for_index( 5 )
>
> If you run this code, you get the following:
>
>>>> print "dir shows that key_for_index %s an attribute of i" % present
>     dir shows that key_for_index is an attribute of i
>>>> i.key_for_index( 5 )
>     Traceback (most recent call last):
>       File "<stdin>", line 1, in ?
>     AttributeError: 'foo' object has no attribute 'key_for_index'
>

That is a bug, I'll look into it. Could you file a bug on SF, just in 
case I forget to fix it :-)

There is one problem with your code: You call the init of only one of 
the superclasses. Because NSObject (obviously) doesn't know about 
Python's multiple inheritance your init should be more like:	

	def init(self):
		self = NSObject.init(self)
		ListManager.init(self)
		return self

Multiple inheritance with Objective-C objects is obviously not used 
very much. And then this bug after I told some people that 
mixin-classes would be a convenient way to add generic implementations 
for protocols (such as NSTableDataSource) to a class :-(

Ronald