Hi All, First of all, I'm not opening a bug yet as I'm not certain whether this is a CPython bug or lxml bug. I'm getting a segfault within python's GC (garbage collector) module. here's the stack trace: #0 0x00007fc7e9f6b76e in gc_list_remove (op=0x7fc79cef3d98) at Modules/gcmodule.c:211 #1 PyObject_GC_Del (op=0x7fc79cef3d98) at Modules/gcmodule.c:1503 #2 0x00007fc7e9f2ac0f in PyEval_EvalFrameEx (f=<value optimized out>, throwflag=<value optimized out>) at Python/ceval.c:2894 #3 0x00007fc7e9ea5b79 in gen_send_ex (arg=None, exc=<value optimized out>, gen=<value optimized out>) at Objects/genobject.c:84 #4 0x00007fc7e9ea6185 in gen_close (self=<generator at remote 0x7fc7c1ba73c0>) at Objects/genobject.c:130 #5 gen_del (self=<generator at remote 0x7fc7c1ba73c0>) at Objects/genobject.c:165 #6 0x00007fc7e9ea5a1b in gen_dealloc (gen=0x7fc7c1ba73c0) at Objects/genobject.c:32 In order to see what object the gc is freeing i tried casting it to a PyObject (we're freeing a lxml object): (gdb) p (PyObject*) op $17 = <ml.etree.DocInfo.standalone.__get__ at remote 0x7fc79cef3d98> Similar bugs (http://osdir.com/ml/python.bugs/2000-12/msg00214.html) blame the extension module for calling dealloc explicitly more than once or doing forbidden things in __del__. this is how i use lxml: from lxml.etree import iterparse def safe_iterparse(*args, **kwargs): for event, element in iterparse(*args, **kwargs): try: yield (event, element) finally: element.clear() I tried parsing the same data but It didn't reproduce.. It happens after a few hours running in production while generating etree using the builder and parsing using the attached code. anyone familiar with these kind of bugs in c extensions/cpython/lxml? could you give pointers to what I should be looking for? should I open a bug? how can I debug lxml? some version info: CPython version: 2.7.2 on linux. lxml: 2.3.3 thanks, Alon Horev