Backport for issue1265 (pdb bug with "with" statement). When an unfinished generator-iterator is garbage collected, PyEval_EvalFrameEx is called with a GeneratorExit exception set. This leads to funny results if the sys.settrace function itself makes use of generators. A visible effect is that the settrace function is reset to None. Another is that the eventual "finally" block of the generator is not called. It is necessary to save/restore the exception around the call to the trace function. This happens a lot with py3k: isinstance() of an ABCMeta instance runs def __instancecheck__(cls, instance): """Override for isinstance(instance, cls).""" return any(cls.__subclasscheck__(c) for c in {instance.__class__, type(instance)}) which lets an opened generator expression each time it returns True. And the problem can be reproduced in 2.5 with pure python code.

/* Return the full version string. */

#include "Python.h"

#include "patchlevel.h"

const char *
Py_GetVersion(void)
{
	static char version[250];
	PyOS_snprintf(version, sizeof(version), "%.80s (%.80s) %.80s", 
		      PY_VERSION, Py_GetBuildInfo(), Py_GetCompiler());
	return version;
}