> I have seen complains from e.g. Tarek that os.urandom() fails under high load: https://twitter.com/tarek_ziade/status/362281268215418880

dev_urandom_python() should handle ENFILE and ENOENT differently to raise a different exception. Or it should always call PyErr_SetFromErrno(PyExc_OSError); ?

Can tarek tell us more about its usecases: is he directly calling os.urandom() or does he use the random module? How many threads?

> How about os.urandom() uses a persistent file descriptor?

os.urandom() is called at Python startup to generate a "secret key" for random hash. If the file descriptor is never closed, the next file descriptor will be 4 instead of the expect 3.

Always keeping an internal file descriptor open may have unexpected effects like leaking a file descriptor to a child process... (see the PEP 446, not implemented yet).

I'm ok to keep a fd open if the user controls the lifetime of the object (lifetime of the fd). For example, I expect that rng = SystemRandom() opens /dev/urandom when the object is created, and closes it when the object is destroyed.