New submission from STINNER Victor <vstin...@python.org>:
The random.Random class has a strange inheritance which is something uncommon in Python: it inherits from _random.Random which a concrete Mersenne Twister PRNG. When a class inherit it, like random.SystemRandom, it should carefully override the right method. I would expect to have something like a base class with abstract methods which raise NotImplementedError, and a concrete implementation which inherits from the base class and the Mersenne Twister C implementation. A concrete issue is the how subclass handle the newly added randbytes() method: https://bugs.python.org/issue40286#msg366860 The base class should implement randbytes() using getrandbits(), and the Mersenne Twister would override randbytes() with its fast implementation. It would avoid the need for such method: def __init_subclass__(cls, /, **kwargs): """Control how subclasses generate random integers. The algorithm a subclass can use depends on the random() and/or getrandbits() implementation available to it and determines whether it can generate random integers from arbitrarily large ranges. """ for c in cls.__mro__: if '_randbelow' in c.__dict__: # just inherit it break if 'getrandbits' in c.__dict__: cls._randbelow = cls._randbelow_with_getrandbits break if 'random' in c.__dict__: cls._randbelow = cls._randbelow_without_getrandbits break It would also be nice if the base class would support a RNG which only produce bytes, like SystemRandom with os.urandom() and implement getrandbits() from that. I also had concerns with the implementation of bpo-40282 "Allow random.getrandbits(0)": https://github.com/python/cpython/pull/19539#pullrequestreview-393728231 It's maybe time to fix the class hierarchy. ---------- components: Library (Lib) messages: 366892 nosy: vstinner priority: normal severity: normal status: open title: Redesign random class inheritance versions: Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue40346> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
