On Fri, Jan 13, 2012 at 5:43 PM, Guido van Rossum <gu...@python.org> wrote: >> How pathological do you consider the set >> >> {1 << n for n in range(2000)} >> >> to be? What about the set: >> >> ieee754_powers_of_two = {2.0**n for n in range(-1074, 1024)} >> >> ? The > 2000 elements of the latter set have only 61 distinct hash >> values on 64-bit machine, so there will be over 2000 total collisions >> involved in creating this set (though admittedly only around 30 >> collisions per hash value). > > Hm... So how does the collision counting work for this case?
Ah, my bad. It looks like the ieee754_powers_of_two is safe---IIUC, it's the number of collisions involved in a single key-set operation that's limited. So a dictionary with keys {1<<n for n in range(2000)} is fine, but a dictionary with keys {1<<(61*n) for n in range(2000)} is not: >>> {1<<(n*61):True for n in range(2000)} Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 1, in <dictcomp> KeyError: 'too many hash collisions' [67961 refs] I'd still not consider this particularly pathological, though. -- Mark _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com