The crash occurs in _asyncio_Future_get_loop():

(gdb) frame
#0  0x00007fffea2fe689 in _Py_INCREF (op=0x0) at ./Include/object.h:459
459	    op->ob_refcnt++;

(gdb) up
#1  0x00007fffea301b14 in _asyncio_Future_get_loop_impl (self=0x7fffea2615f0)
    at /home/vstinner/python/master/Modules/_asynciomodule.c:1094
1094	    Py_INCREF(self->fut_loop);

(gdb) p self->fut_loop
$1 = 0x0

(gdb) where
#0  0x00007fffea2fe689 in _Py_INCREF (op=0x0) at ./Include/object.h:459
#1  0x00007fffea301b14 in _asyncio_Future_get_loop_impl (self=0x7fffea2615f0)
    at /home/vstinner/python/master/Modules/_asynciomodule.c:1094
#2  0x00007fffea2fef01 in _asyncio_Future_get_loop (self=0x7fffea2615f0, 
    _unused_ignored=0x0)
    at /home/vstinner/python/master/Modules/clinic/_asynciomodule.c.h:252
#3  0x0000000000645364 in cfunction_vectorcall_NOARGS (
    func=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>, 
    args=0x0, nargsf=0, kwnames=0x0) at Objects/methodobject.c:424
#4  0x000000000042f8d1 in _PyObject_VectorcallTstate (tstate=0x81ae00, 
    callable=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>, args=0x0, nargsf=0, kwnames=0x0) at ./Include/cpython/abstract.h:111
#5  0x000000000042f930 in _PyObject_Vectorcall (
    callable=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>, args=0x0, nargsf=0, kwnames=0x0) at ./Include/cpython/abstract.h:120
#6  0x000000000042f988 in _PyObject_CallNoArg (
    func=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>)
    at ./Include/cpython/abstract.h:148
#7  0x000000000042fc57 in PyObject_CallNoArgs (
    func=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>)
    at Objects/call.c:83
#8  0x00007fffea2ffc16 in get_future_loop (
    fut=<Qwe2(value=0) at remote 0x7fffea2615f0>)
--Type <RET> for more, q to quit, c to continue without paging--q
Quit

(gdb) py-bt
Traceback (most recent call first):
  <built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>
  <built-in method run of Context object at remote 0x7fffea215170>
  File "/home/vstinner/python/master/Lib/asyncio/events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "/home/vstinner/python/master/Lib/asyncio/base_events.py", line 2641, in _run_once
  File "/home/vstinner/python/master/Lib/asyncio/base_events.py", line 1101, in run_forever
    await waiter
  File "/home/vstinner/python/master/Lib/asyncio/base_events.py", line 621, in run_until_complete
    self.run_forever()
  File "/home/vstinner/python/master/Lib/asyncio/runners.py", line 299, in run
  File "/home/vstinner/python/master/scratch_15.py", line 56, in <module>
    asyncio.run(main())