By the way, the crash involves an _ElementInterface subclass named SimpleElementTreeVar:

#0  0x0000000000524c0f in visit_decref (op=Traceback (most recent call last):
  File "/home/antoine/cpython/33/python-gdb.py", line 1298, in to_string
    pyop = PyObjectPtr.from_pyobject_ptr(self.gdbval)
  File "/home/antoine/cpython/33/python-gdb.py", line 370, in from_pyobject_ptr
    cls = cls.subclass_from_type(p.type())
  File "/home/antoine/cpython/33/python-gdb.py", line 318, in subclass_from_type
    tp_name = t.field('tp_name').string()
  File "/usr/lib64/python2.7/encodings/utf_8.py", line 16, in decode
    return codecs.utf_8_decode(input, errors, True)
UnicodeDecodeError: 'utf8' codec can't decode byte 0x95 in position 1: invalid start byte
, data=0x0) at Modules/gcmodule.c:361
#1  0x00000000005bcbc5 in BaseException_traverse (self=0x7f08f390a8b0, visit=0x524b98 <visit_decref>, arg=0x0)
    at Objects/exceptions.c:104
#2  0x00000000004336d9 in subtype_traverse (self=
    <SimpleElementTreeVar(attrib={}, tag='root', ourValue=None, _children=[]) at remote 0x7f08f390a8b0>, 
    visit=0x524b98 <visit_decref>, arg=0x0) at Objects/typeobject.c:837
#3  0x0000000000524cba in subtract_refs (containers=0x8dcf40) at Modules/gcmodule.c:386
#4  0x0000000000525afa in collect (generation=0, n_collected=0x7fffed18be00, n_uncollectable=0x7fffed18bdf8)
    at Modules/gcmodule.c:891
#5  0x00000000005260b2 in collect_with_callback (generation=0) at Modules/gcmodule.c:1048
#6  0x000000000052615c in collect_generations () at Modules/gcmodule.c:1071
#7  0x000000000052707d in _PyObject_GC_Malloc (basicsize=48) at Modules/gcmodule.c:1580
[snip]