John Ehresman <[EMAIL PROTECTED]> writes:
> The following causes a seg fault because it attempts to reference a CTree
> node which does not exist:
>
> >>> import gtk
> >>> tree = gtk.GtkCTree()
> >>> n = tree.node_nth(10)
> >>> print n.parent
>
> Looking at the source, it appears that the C api function returns NULL in
> this case, but this pointer is passed to PyGtkCTreeNode_New. The pointer
> is then stored and dereferenced in the get attr function, causing the seg
> fault. There are a couple ways to fix this that are relatively easy to
> implement:
> * Return None if the pointer is NULL.
> * Throw an exception if NULL is returned.
>
> My question is which is the preferred method in this case and whether all
> the cases where a node is returned should be handled the same way -- are
> there cases where NULL would be an acceptable value rather than a result
> of passing incorrect values to function. Also, should other boxed types
> act the same way.
The code for these functions is generated by a python program from
some sort of specification. I have appended a patch that checks for
NULL values when returning a (GtkObject *) and in that case returns
None.
A problem with throwing exceptions is that some generated functions
can return NULL as a valid value, and in other cases its clearly a
program error. One way to solve this would be to provide info to the
generator about each function that should raise an exception. Maybe
its a better solution to not change the generator but change some
wrappers in gtk.py to raise an excpetion on a None return.
todo: look for other types that should be handled in the same way
Index: generate.py
===================================================================
RCS file: /cvs/gnome/gnome-python/pygtk/generate/generate.py,v
retrieving revision 1.2
diff -u -r1.2 generate.py
--- generate.py 1999/02/19 03:48:37 1.2
+++ generate.py 1999/12/15 07:41:06
@@ -421,9 +421,12 @@
impl.write(funcCall)
impl.write(');\n')
elif retType in objects.keys():
- impl.write(' return PyGtk_New((GtkObject *)')
- impl.write(funcCall)
- impl.write(');\n')
+ impl.write(' {\nGtkObject *p = (GtkObject *)%s;\n'
+ % funcCall)
+ impl.write(' if (p)\n')
+ impl.write(' return PyGtk_New(p);\n}\n')
+ impl.write(' Py_INCREF(Py_None);\n')
+ impl.write(' return Py_None;\n')
else:
print "%s: unknown return type '%s'" % (name, retType)
return 1
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