Choose random seed and save it

Question

I would like to choose a random seed for numpy.random and save it to a variable. I can set the seed using numpy.random.seed(seed=None) but how do you

Answer 1

According to the docs, when seed is None, numpy tries to read from /dev/urandom, so why not just read a value from /dev/urandom, save it, and pass it to numpy.random.RandomState?

EDIT:

The internal state can be get and set via get_state and set_state, respectively. So, to recover the initial state, one would do something like this:

>>> import numpy
>>> r = numpy.random.RandomState()
>>> saved_state = r.get_state()
>>> r.rand()
0.9091545657342729
>>> r.rand()
0.9677739782319564
>>> r.rand()
0.5656156400920441
>>> r.set_state(saved_state)
>>> r.rand()
0.9091545657342729
>>> r.rand()
0.9677739782319564
>>> r.rand()
0.5656156400920441
>>> 

When seed is None, numpy doesn't pick a "new random seed" and call seed() with it. It reads 624 * sizeof(long) bytes (~ 2.5KB) from /dev/urandom and uses those values to populate the state struct. When you call seed() without arguments, numpy never actually "chooses" a "random seed". Therefore, it's not possible to recover it.