Does Python have a library that produces data as fast os.urandom but is reproducible?

Question

Is there a Python library that can produce random data as fast as os.urandom, but the data can be reproduced if given a seed?

How did your search on "Python random seed" not turn up the hits? — Prune
– Prune, Commented Apr 2, 2018 at 18:21
You do know the difference between what os.urandom does and pseudo-random generators do, right? — Jon Clements
– Jon Clements, Commented Apr 2, 2018 at 18:22
The speeds given by pv < /dev/urandom > /dev/null vary significantly between systems. Mine cluster around ~13MiB/s, with one producing ~180MiB/s. These aren't particularly fast rates. What are you going to be using this random data for? — Blender
– Blender, Commented Apr 2, 2018 at 18:30
I know that os.urandom is totally random, but I could not find a suitable pseudo-random generator that did a similar thing. I'm using the data to test write functionality to a bunch of luns. — Laharl
– Laharl, Commented Apr 2, 2018 at 18:53

Blender · Accepted Answer · 2018-04-02 23:00:43Z

You can use random.seed to produce a reproducible sequence. The only problem is getting Python to produce random bytes quickly. You can use a trick observed by @jfs with random.getrandbits to reduce the amount of processing Python has to do:

import random def almost_urandom(n): return random.getrandbits(8 * n).to_bytes(n, 'big')

random.seed lets you deterministically generate the bytes:

In [26]: random.seed(0) In [27]: almost_urandom(10) Out[27]: b'\xc2\tb\x9fo\xbe\xd8,\x07\xcd' In [28]: almost_urandom(10) Out[28]: b'\n]k\xaa\x94U\xe3\xe7\x06\x82' In [29]: random.seed(0) In [30]: almost_urandom(10) Out[30]: b'\xc2\tb\x9fo\xbe\xd8,\x07\xcd' In [31]: almost_urandom(10) Out[31]: b'\n]k\xaa\x94U\xe3\xe7\x06\x82'

It runs an order of magnitude faster than os.urandom() for me, even for n in the millions.

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