>>> import trio
>>> async def main():
...     with trio.CancelScope() as cs:
...         try:
...             async with trio.open_nursery() as nursery:
...                 nursery.cancel_scope.cancel()
...                 cs.cancel()
...                 await trio.lowlevel.checkpoint()
...         except trio.Cancelled as e:
...             print("cancelled:")
...             print(repr(e.__context__))
...
>>> trio.run(main)
>>> async def main():
...     with trio.CancelScope() as cs:
...         try:
...             with trio.CancelScope() as cs2:
...                 cs2.cancel()
...                 cs.cancel()
...                 await trio.lowlevel.checkpoint()
...         except trio.Cancelled as e:
...             print("cancelled:")
...             print(repr(e.__context__))
...
>>> trio.run(main)
cancelled:
None