A crucial difference between a set and a type is that you cannot explicitly iterate over the elements of a type, so while we could implement
x in int to do something useful, we cannot make for x in int: print(x) Because if we could, we could implement Russell's paradox in Python: R = set(x for x in object if x not in x) print(R in R) Bottom line: a set is not a type, even in mathematics. Stephan 2017-03-02 5:38 GMT+01:00 Pavol Lisy <[email protected]>: > On 3/1/17, Steven D'Aprano <[email protected]> wrote: > > On Wed, Mar 01, 2017 at 07:02:23AM +0800, 语言破碎处 wrote: > >> > >> where we use types? > >> almost: > >> isinstance(obj, T); > >> # issubclass(S, T); > >> > >> Note that TYPE is SET; > > > > What does that mean? I don't understand. > > Maybe she/he wants to say that it is natural to see class as a > collection (at least in set theory > https://en.wikipedia.org/wiki/Class_(set_theory) ) > _______________________________________________ > Python-ideas mailing list > [email protected] > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
_______________________________________________ Python-ideas mailing list [email protected] https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
