> I encounter a quite similar issue with python 3.4.0 and cx_Oracle.

Your issue is different, compare the top frames:

My trace:

#0  0x0000003f3a835c59 in raise () from /lib64/libc.so.6
#1  0x0000003f3a837368 in abort () from /lib64/libc.so.6
#2  0x0000003f3a82ebb6 in __assert_fail_base () from /lib64/libc.so.6
#3  0x0000003f3a82ec62 in __assert_fail () from /lib64/libc.so.6
#4  0x000000000043ac66 in visit_decref (
    op=Frame 0x7f013c001398, for file x.py, line 43 (...) at Modules/gcmodule.c:379
#5  0x00000000004336bd in tb_traverse (tb=0x7f01493a66e8, visit=0x43abb4 <visit_decref>, arg=0x0) at Python/traceback.c:64
#6  0x000000000043acdc in subtract_refs (containers=0x8f1a20 <generations+64>) at Modules/gcmodule.c:398

cx_Oracle trace:

#0  0x000000000043ab98 in visit_decref (op=0xb00000000, data=0x0) at Modules/gcmodule.c:373
#1  0x000000000048193a in BaseException_traverse (self=0x7ffff0f645f8, visit=0x43ab64 <visit_decref>, arg=0x0) at Objects/exceptions.c:97
#2  0x00000000004dc4cc in subtype_traverse (self=0x7ffff0f645f8, visit=0x43ab64 <visit_decref>, arg=0x0) at Objects/typeobject.c:972

In my trace, visit_decref() is called on a frame and fail with an assertion error.

In cx_Oracle trace, visit_decref() is called on a NULL pointer which comes from an Exception.

In my experience, it's a bug in cx_Oracle. If you think that I'm wrong and that it's a bug in Python, please open a *new* issue since the trace is different.

--

For your cx_Oracle, issue:

#1  0x000000000048193a in BaseException_traverse (self=0x7ffff0f645f8, visit=0x43ab64 <visit_decref>, arg=0x0) at Objects/exceptions.c:97

Can you go this frame (in gdb, type "frame 1") and dump the Exception object:

(gdb) print _PyObject_Dump(0x000000000048193a)

Note for myself: I should write a documentation explaining how to debug Python in gdb.