Re: [Pyobjc-dev] Using python classes in objc...

[b.bum <bb...@ma...>]

On Mar 10, 2004, at 9:01 AM, Jiva DeVoe wrote:
> How do I get around this problem?  BBum has mentioned using a factory 
> method in an abstract superclass.  Ok, that's fine, but even then, the 
> factory method still has to instantiate the python class.  How does it 
> do so without linking the python code?

Do something like:

@implementation MyFactoryAbstractObjCClassyThing
+ createAConcreteInstance
{
	Class aClass = 
NSClassFromString(@"ConcretePythonSubclassOfThisClass"); // only works 
if you had previously imported the appropriate code in python

	return [[aClass alloc] init];
}

To avoid compiler warnings when messaging the class, you can:

- declare the methods on a category of the abstract super.   Categories 
do not have to have an associated implementation.  Alternatively, you 
can provide abstract implementations of the methods that do something 
like:

- (void) methodThatIsReallyImplementedInPython
{
	@throw [NSException exceptionWithName: 
NSInternalInconsistencyException reason: @"Subclass must implement 
this." userInfo: nil];
}

- use -performSelector:, -performSelector:with: and friends to 
indirectly invoke the method

- make all your functionality Key-Value Coding and use Bindings and/or 
-setValue:forKey: and -valueForKey: (not really practical for anything 
but data passing)

- use NSInvocation to build up the method invocation

I generally go with the first option:

@interface Abstract:NSObject
+ instatiateSubclassNamed: (NSString *) aClassName;
@end

@interface Abstract(MethodsThatMustBeInPythonSubclass)
...
@end

Then, in python:

class Foo(Abstract)
	def ....: