From the python-dev thread:

http://mail.python.org/pipermail/python-dev/2010-October/104782.html

“os._exit is useful. os.open is useful. aio_* are *not* useful. For anything. If there's anything you think you want to use them for, you're wrong. It either won't work properly or it will worse performing than the simpler alternatives.”

http://mail.python.org/pipermail/python-dev/2010-October/104786.html

“I'd like to echo this sentiment.  This is not about providing a 'safe' wrapper to hide some powerful feature of these APIs: the POSIX aio_* functions are really completely useless.

[...]

Not only is the performance usually worse than expected, the behavior of aio_* functions require all kinds of subtle and mysterious coordination with signal handling, which I'm not entirely sure Python would even be able to pull off without some modifications to the signal module.  (And, as Jean-Paul mentioned, if your OS kernel runs out of space in a queue somewhere, completion notifications might just never be delivered at all.)”