Add strategy for numpy.random.Generator

[rsokl]

Partially addressing #3131 (only a year later...), this adds hypothesis.extra.rand_generators for generating numpy.random.Generator instances with Hypothesis-controlled seeds. These have specialized reprs that enable reproducibility. This bumps our minimum supported version of NumPy to 1.19.0¹. 1.19.0 has already dropped out of the NEP 29 support window, so I do not think that this is an unreasonable dependency bump.

>>> from hypothesis.extra.numpy import rand_generators
>>> [rand_generators().example() for _ in range(3)]
[Generator(PCG64(17731618377865219412)),
Generator(PCG64(16938332804403789103)),
Generator(PCG64(9641801721570554589))]

>>> from numpy.random import MT19937, PCG64
>>> # specifying multiple backing bit-generator types
>>> [rand_generators(MT19937, PCG64).example() for _ in range(3)]
[Generator(PCG64(1138900339423482065)),
Generator(MT19937(13796052070681794055)),
Generator(MT19937(16637614687104877655))]

Once #3509 is merged, I can add numpy.random.Generator support for register_random (I figured out how to make the compatibility shim work)

Footnotes

1. When BitGenerator was added to the NumPy's public API ↩

[Zac-HD]

Just dumping thoughts here:

• if we're bumping the Numpy version, let's make sure that using something too old is an explicit error - and link to NEP-29. We could in principle support older versions of Numpy in everything but RNG; I don't think it's worth it
• I think we should probably replicate the st.randoms(*, note_method_calls=False, use_true_random=False) interface. This is going to be pretty annoying, but IMO it's a pretty useful feature for shrinking and therefore debuggability. Unfortunately since the default is to draw from Hypothesis instead we can't backfill that in a future PR without changing behavior...
• Relatedly, we could easily drop in a HypothesisBitGenerator() shim; this might be a good first pass at the above. Long-term I think we want a HypothesisGenerator class so that generated sizes, floats, etc. shrink as we'd want them to.

I realize that this amounts to asking for substantial extra work, sorry! Happy to try to find a workable subset if it's too much.

Finally, when you say "partially addressing", what will be left after this PR? It'd be nice to have a checklist, or perhaps close the issue and open a newer and more-specific one 😁

[Zac-HD]

Closing this as stale 😥