Re: extra_ivars assersion failure

On 28/08/2003 6:33 AM, Ben Liblit wrote:

> I'm having trouble subclassing a class from an extension module.  When 
> Python processes my subclass definition, and before any instances are 
> created, it aborts with:
>
>     python: Objects/typeobject.c:872: extra_ivars:
>     Assertion `t_size >= b_size' failed.
>
> The extension module is trying to coordinate no less than three 
> different object systems (GObject, CORBA, Python).  Let me back up and 
> explain what's going on in there.
>
> In the world of the GTK+ GObject system, I've got a GObject subclass. 
> (It's actually a subclass of BonoboObject, which in turn derives from 
> GObject.)  I can write C code that instantiates this GObject-derived 
> class and all is well.
>
> I'm wrapping these GObject instances inside Python objects using 
> h2def.py and pygtk-codegen-2.0.  The ".defs" file looks good: there's 
> a define-object construct with the right class name and parent class 
> name.  The constructor is detected and wrapped correctly.  In the 
> ".override" file I "import bonobo.Object as PyBonoboObject_Type", and 
> everything builds smoothly.  I can write Python code that instantiates 
> this wrapper class and all is well.
>
> What I cannot do is subclass this wrapper class in Python code.  When 
> I try to, I get the diagnostic message reported earlier:
>
>     python: Objects/typeobject.c:872: extra_ivars:
>     Assertion `t_size >= b_size' failed.
>
> Does anyone know what deeper problem this message is symptomatic of? 
> What am I doing wrong in my extension module that would allow it to 
> work correctly when the wrapper class is instantiated directly, but 
> which would cause this error when a subclass of the wrapper class is 
> defined?

It sounds like the size of your object (tp_basicsize) is smaller than 
the size of your base class.  Python raises an assertion here because it 
would mean that methods of the base class may try to access unallocated 
memory when presented an instance of the subclass.

Take a look at the examples in the Python descriptor intro document 
about how to subclass from something like list.  That should give an 
idea of what to do in this case.

James.

--
Email: james@xxxxxxxxxx
WWW:   http://www.daa.com.au/~james/



_______________________________________________
pygtk mailing list   pygtk@xxxxxxxxxx
http://www.daa.com.au/mailman/listinfo/pygtk
Read the PyGTK FAQ: http://www.async.com.br/faq/pygtk/