[Pyobjc-dev] __getitem__objectForKey_ shadows __getitem__

[James R E. <Jam...@lr...>]

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