Re: [Pythonmac-SIG] creating PyObjC wrapper for ObjC framework?

[Ronald Oussoren]

On 10 Jan, 2008, at 18:00, has wrote:

On 10 Jan 2008, at 06:54, Ronald Oussoren wrote:

I'm trying to create a PyObjC wrapper for objc-appscript,

Why?

Partly just to know how, as one of objc-appscript's goals is to
provide a foundation for implementing other appscript bridges, and
this lets me explore the ins and outs.


Partly so I can do casual testing in an interactive interpreter.
(Yeah, I'm a slob.)

Using Python for unittest an interactive exploration is actually a major usecase for PyObjC, so don't feel to bad about this ;-)

Partly because I've been toying with the idea of having objc-aem
provide the basis for appscript support in Jonathan Wight's PyObjC-
based 'Run Python Script' Automator action.

and I'm
wondering how to wrap methods that have NSError** arguments, e.g.:

The easiest way is to mark the arguments as 'out' in the Objective-C
prototype (and then recompile), that way PyObjC will pick up the
right metadata from the ObjC runtime and you won't need the
bridgesupport file

Ahh, too easy. Duh.

I keep trying to make it as easy as possible to create Objective-C code that is trivial to wrap using PyObjC, although documentation and advocacy is rather lacking :-(

The logical thing would be to convert a returned NSError into a
Python
exception, but BridgeSupport's gen_bridge_metadata tool doesn't seem
to provide any help here, simply flagging the argument as 'opaque'.
Any advice on how to proceed (with or without using BS)?

Don't try to convert the NSError to an exception, that would make
your wrapper complete different from other wrappers and hence more
likely to cause confusion for users.

Okay. (Is this something that's changed since PyObjC 1.x, or is my
memory just playing tricks?)

Cocoa basicly has two ways to do structured error handling:


   raises an exception)





Python uses exceptions for all of these.

Ronald

That's probably just your memory. NSException's are bridged to Python exceptions, that may cause the confusion. * Exceptions, which are basicly only used for handling programmer errors (trying to change a immutable dictionary * NSErrors, which are used for everything else (OS Errors, running out of resources, ...) * Several ancient API's use strings instead of NSErrors. (I know, this is item 3 in a 2 item list)

Thanks,

has
--
http://appscript.sourceforge.net
http://rb-appscript.rubyforge.org

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