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.

/* Portable fmod(x, y) implementation for systems that don't have it */

#include "pyconfig.h"

#include "pyport.h"
#include <errno.h>

double
fmod(double x, double y)
{
	double i, f;
	
	if (y == 0.0) {
		errno = EDOM;
		return 0.0;
	}
	
	/* return f such that x = i*y + f for some integer i
	   such that |f| < |y| and f has the same sign as x */
	
	i = floor(x/y);
	f = x - i*y;
	if ((x < 0.0) != (y < 0.0))
		f = f-y;
	return f;
}