[Pythonmac-SIG] I think I just ate a Zombie

Ronald Oussoren ronaldoussoren at mac.com
Fri May 5 00:25:19 CEST 2006


On 4-mei-2006, at 14:47, Saggau wrote:

I haven't look at your example just yet, will do that later on. I'm  
happy you took the time to create a small program that demonstrates  
the problem you're seeing, that makes is so much easier to search the  
problem.

> What did I learn from this:
>
> 1. Try to use cocoa objects instead of python objects in code that  
> uses bindings; pay special attention to collections (lists, etc.).  
> At least this *seems* safer because a python object being  
> referenced from cocoa is probably more likely to cause problems  
> than a cocoa object controlled from python. (?) Then again, it's  
> pretty stupid to generalize from one experience...

Using Cocoa datastructures instead of python ones when KVO is  
involved is always a good idea. Python doesn't have enough hooks to  
allow reliable interception __setitem__. We could (but don't)
get 95% of the way by using the same class-swiffling technique as  
used by the ObjC runtime, but could never go all the way.

> 2. GDB is very useful for debugging pyobjc.
> 3. There are a lot of nice pyobjc debugging features, but you have  
> to turn them on (See my example project referenced above).
>
> Things I want to know:
> 1. Is there a way, when one gets the memory address of a pyobjc  
> proxy object (Like OC_PythonArray) from gdb to figure out which  
> python object it's proxying?
The PyObject* is stored as the instance variable 'value' on the proxy  
object.

> 2.  Is there a way to get the python object from a memory address?

You mean like "(PyObject*)0xDEADBEEF"?

> 3. Is there a reliable way to get (in gdb or pdb) the "Python List  
> Object at 0x03423blahblahblah information from the python object  
> being proxied

> 4. Can I compile pyobjc with debugging symbols? GDB without them  
> hurts my brain.

PyObjC is compiled with debugging symbols by default. Py2app strips  
debugging symbols, unless you build with the -A flag.

Ronald

> Cheers,
> Jonathan Saggau
>
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