> Making it easy to create subclasses was never a goal regardless.

It's clearly advertised at the beginning of the documentation:

"Class Random can also be subclassed if you want to use a different basic generator of your own devising: (...)"

Do you mean that the documentation is wrong and users must not subclass random.Random?


> If that makes any method currently in use slower, it's not worth it.

I don't think that my PR 19631 has any impact on random.Random and random.SystemRandom performances. Only new 3rd party classes which will be written to inherit from the *new* random.BaseRandom loose the gauss() optimization.

It would be possible to keep the optimization, but it would make class inheritance more complex: subclasses would have to call seed(), getstate() and setstate() methods of BaseRandom. Moreover, I dislike that the base class is not thread state. I prefer to keep it simple and correct.


> that reworking this doesn't solve any actual problem.

I changed the issue title to clarify my intent.

My intent is to ease the creation of subclasses. In Python 3.8, a subclass has to *override* 5 methods: getrandbits(), random(), seed(), getstate() and setstate().

With the proposed BaseRandom, a sublcass only has to *implement* *1* single method, getrandbits():

* random() and randbytes() are implemented with getrandbits() automatically
* seed(), getstate() and setstate() raise NotImplementedError, as done by SystemRandom currently. Obviously, you can override them if you want. But at least, you don't inherit the whole Mersenne Twister state by default.

The current problem is that Python 3.9 adds randbytes() which means that a class which inherit from random.Random now has to override not 5 but 6 methods: it now also has to override randbytes().

Raymond proposes to remove _random.Random.randbytes() C implementation and use instead a Python implementation which is 5x slower.

For me, it's surprising that if a subclass doesn't override all methods, it gets a Mersenne Twister implementation. See my msg366918 example. I would prefer a real base class with has no default implementation.

It doesn't prevent people to continue to inherit from random.Random: classes which inherit from random.Random continue to work.

Note: currently in my PR 19631, seed() has to be implemented since it's called by the constructor. I'm not sure if it's a good design or not.