The following code (extracted from test_extcall.py) leaks memory: class Foo: def method(self, arg1, arg2): return arg1 + arg2 def f(): err = None try: Foo.method(*(1, 2, 3)) except TypeError, err: pass del err One-line fix (also posted to Sourceforge): --- Python/ceval.c 2000/10/30 17:15:19 2.213 +++ Python/ceval.c 2000/12/14 20:54:02 @@ -1905,8 +1905,7 @@ class))) { PyErr_SetString(PyExc_TypeError, "unbound method must be called with instance as first argument"); - x = NULL; - break; + goto extcall_fail; } } } I think that there are a bunch more memory leaks lurking around... this only fixes one of them. I'll send more info as I find out what's going on.