On Sat, Dec 18, 2021 at 1:21 AM Hao Hu <hao.hu...@gmail.com> wrote: > > Hi, > > I am wondering if it would be good to add an additional keyword `seed` to the > builtin function *hash* to allow us to set arbitrary seed to ensure > reproducible results. >
The built-in hash() function is extremely generic, so it can't really work that way. Adding a parameter to it would require (a) adding the parameter to every __hash__ method of every object, including user-defined objects; and (b) defining what that would mean when multiple objects' hashes are combined (eg hashing a tuple). > > As far as I know, there exists already the environment variable > PYTHONHASHSEED that allows us to set arbitrary seed or disable the seed > globally for the python interpreter. > However, it looks like that it would be too bold to use that environment > variable to change the default behavior because the random seed generation > helps improve the security my reducing the risk of hash flooding. > > In parallel, we have identified a couple of real use cases that require that > an arbitrary seed is used for a limited scope. > For instance, if we create a caching programming interface that relies on a > distributed kv store, it would be very important to make sure that the hash > key stays the same when the application is rebooted or replicated. It is > generally more cautious to use the above capability to limit the scope to the > caching library itself instead of applying the same for all the hash > functions of all the python interpreters. > For that sort of thing, it may be more practical to use your own hashing function, possibly a cryptographically secure one. The precise hashing function used by Python isn't guaranteed, so if you need it to be stable across different runs, and especially if you need to seed it in a specific way, I'd recommend hashlib: https://docs.python.org/3/library/hashlib.html ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/CU4TI3AEMI7Y6USIIHDWWSQW7WGGPNJ7/ Code of Conduct: http://python.org/psf/codeofconduct/
