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In gdb we supply a class whose nb_int method can throw
an exception.
A user wrote code like this:
 return '%x' % value
... where "value" was an instance of this class.
This caused funny exception behavior later on.
You can see the original report here:
http://sourceware.org/bugzilla/show_bug.cgi?id=14320
I tracked down the odd behavior to this code in
stringobject.c:PyString_Format:
 iobj = PyNumber_Int(v);
 if (iobj==NULL) iobj = PyNumber_Long(v);
Here, PyNumber_Int fails and sets the exception.
I think this ought to be cleared before calling
PyNumber_Long. In our case, PyNumber_Long succeeds,
and the program keeps executing until something happens
to call PyErr_Occurred.
I think this patch ought to fix the problem:
diff -r e0eb7dea245f Objects/stringobject.c
--- a/Objects/stringobject.c	Mon Jul 30 04:07:49 2012 -0700
+++ b/Objects/stringobject.c	Tue Jul 31 13:58:07 2012 -0600
@@ -4489,7 +4489,10 @@
 }
 else {
 iobj = PyNumber_Int(v);
- if (iobj==NULL) iobj = PyNumber_Long(v);
+ if (iobj==NULL) {
+			 PyErr_Clear();
+			 iobj = PyNumber_Long(v);
+			}
 }
 if (iobj!=NULL) {
 if (PyInt_Check(iobj)) {
I haven't written a test case yet; David Malcolm suggested I file
a bug here first.