When running asyncio in debug mode (e.g. by setting environment variable 
PYTHONASYNCIODEBUG) and trying Task.get_stack, an exception is raised because 
the _CoroWrapper class is not a generator (I assume, not an expert on generator 
internals). The attached file will reproduce this issue on asyncio 0.4.1.

The exception produced looks like this:
Traceback (most recent call last):
  File "asyncio_stack_exc.py", line 14, in <module>
    loop.run_until_complete(test_outer())
  File "/home/javex/.virtualenvs/misc/lib/python3.3/site-packages/asyncio/base_events.py", line 208, in run_until_complete
    return future.result()
  File "/home/javex/.virtualenvs/misc/lib/python3.3/site-packages/asyncio/futures.py", line 243, in result
    raise self._exception
  File "/home/javex/.virtualenvs/misc/lib/python3.3/site-packages/asyncio/tasks.py", line 283, in _step
    result = next(coro)
  File "/home/javex/.virtualenvs/misc/lib/python3.3/site-packages/asyncio/tasks.py", line 50, in __next__
    return next(self.gen)
  File "/home/javex/.virtualenvs/misc/lib/python3.3/site-packages/asyncio/tasks.py", line 84, in coro
    res = func(*args, **kw)
  File "asyncio_stack_exc.py", line 11, in test_outer
    t.print_stack()
  File "/home/javex/.virtualenvs/misc/lib/python3.3/site-packages/asyncio/tasks.py", line 228, in print_stack
    for f in self.get_stack(limit=limit):
  File "/home/javex/.virtualenvs/misc/lib/python3.3/site-packages/asyncio/tasks.py", line 197, in get_stack
    f = self._coro.gi_frame
AttributeError: 'CoroWrapper' object has no attribute 'gi_frame'

The source of the issue (roughly) is this line: 
https://code.google.com/p/tulip/source/browse/asyncio/tasks.py#91

I think the most easy (but not necessarily the best) fix would be to modify the 
"get_stack" method to check whether "self._coro" 
(https://code.google.com/p/tulip/source/browse/asyncio/tasks.py#197) is an 
instance of CoroWrapper (in the same manner the former half of iscoroutine 
works https://code.google.com/p/tulip/source/browse/asyncio/tasks.py#110).

So one could do something like this:
if _DEBUG:
    f = self._coro.gen.gi_frame
else:
    f = self._coro.gi_frame

Which should work in this case. However, possibly some other code paths also 
rely on the assumption that the coroutine actually is a generator directly so 
maybe there are other places to fix.