Re: [Pyobjc-dev] __getitem__objectForKey_ shadows __getitem__

[Ronald O. <ron...@ma...>]

James,

PyObjC currently blindly adds its own version of __getitem__ when it detects that a Cocoa class implements objectForKey: or objectAtIndex:.  It should be easy enough to check that the Cocoa class doesn't have its own version of __getitem__ before adding the generic version.

BTW. In the longer run (that is, post 2.2 final) I will remove this logic and switch to class-based logic instead. That is, rather then looking for objectForKey: I'll add a list of classes that will get a __getitem__ implementation. This is slightly less generic, but allows me to optimize method dispatch. 

Ronald
 
On Friday, October 09, 2009, at 02:46PM, "James R Eagan" <Jam...@lr...> wrote:
>Hi folks,
>
>I was trying to be smart in a class that provides both a Cocoa-style  
>and Pythonic interface (i.e. implementing both objectForKey_ and  
>__getitem__ and friends).  It turns out that PyObjC already does that  
>for me (cool!), but in the process of debugging an unrelated fault in  
>my program, I noticed that the implementation in PyObjC will always  
>replace __getitem__ with __getitem__objectForKey_, meaning that it is  
>impossible to combine different lookup behaviors for the Objective-C  
>and Pythonic interfaces.  (I'm haven't yet convinced myself that this  
>is necessarily a bad thing.)  See the following example:
>
>	>>> from Foundation import *
>	>>> import objc
>	>>> class Foo(NSObject):
>	...     def objectForKey_(self, key):
>	...             return 'object for key'
>	...     def __getitem__(self, key):
>	...             return 'getitem'
>	...
>	>>> foo = Foo.alloc().init()
>	>>> foo.objectForKey_('foo')
>	'object for key'
>	>>> foo['foo']
>	'object for key'
>	>>> foo.__getitem__
>	<bound method Foo.__getitem__objectForKey_ of <Foo: 0x370e880>>
>
>
> From what I can tell, the relevant code is in pyobc-core/Lib/objc/ 
>_convenience.py:88 :
>
>         if sel in CONVENIENCE_METHODS:
>             v = CONVENIENCE_METHODS[sel]
>             for nm, value in v:
>                 if nm in type_dict and isinstance(type_dict[nm],  
>selector):
>
>                     # Clone attributes of already existing version
>
>                     t = type_dict[nm]
>                     v = selector(value, selector=t.selector,
>                         signature=t.signature,  
>isClassMethod=t.isClassMethod)
>
>                     type_dict[nm] = v
>                 else:
>                     type_dict[nm] = value
>
>This seems to be a fairly core portion of the PyObjC, and I have not  
>explored the ramifications of modifying the inner if ... else block to  
>only add the convenience methods if the nm is not already in  
>type_dict.  Should that else really be an "elif nm not in type_dict" ?
>
>Cheers!
>James
>
>
>
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