[Numpy-discussion] NEP: Random Number Generator Policy (original) (raw)

Robert Kern robert.kern at gmail.com
Sun Jun 3 20:36:58 EDT 2018

On Sun, Jun 3, 2018 at 4:35 PM Eric Wieser <wieser.eric+numpy at gmail.com> wrote:

You make a bunch of good points refuting reproducible research as an argument for not changing the random number streams.

However, there’s a second use-case you don’t address - unit tests. For better or worse, downstream, or even our own <https://github.com/numpy/numpy/blob/c4813a9/numpy/core/tests/testmultiarray.py#L5093-L5108>, unit tests use a seeded random number generator as a shorthand to produce some arbirary array, and then hard-code the expected output in their tests. Breaking stream compatibility will break these tests. By the way, the reason that I didn't mention this use case as a motivation in the Status Quo section because, as I reviewed my mail archive, this wasn't actually a motivating use case for the policy. It's certainly a use case that developed once we did make these (coughextravagantcough) guarantees, though, as people started to rely on it, and I hope that my StableRandom proposal addresses it to your satisfaction. I could add some more details about that history if you think it would be useful.

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