Reproducer:

from aiohttp.multidict import CIMultiDictProxy, CIMultiDict
import sys

try:
    raise Exception
except Exception:
    print(sys.exc_info())
    repr(CIMultiDictProxy(CIMultiDict()))
    print(sys.exc_info())

Results:

(<class 'Exception'>, Exception(), <traceback object at 0x101a3d048>)
(None, None, None)

This is fairly serious; if you stick an 'as e' at the end of 'except Exception' and a 'raise' at the end of the except block, you wind up with a segfault.

Discovered in version 0.14.4, confirmed in 0.16.3.