Cleanest way to get a random number inside pypy sandbox?

I'm wondering what the easiest source of randomness inside a pypy sandbox is.

Things I've tried:

• Random library
• Time library
• Reading from /dev/random
• os.urandom()

The best solution I have now is to make a class which is initialized with a seed, and this seed is just incremented every time the instance is asked for a random number, and using some pseudo-random generation algorithm. I don't need very good randomness, so this isn't terrible, but it still seems pretty ugly.

I believe anything in pure Python should work.