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 <pavol.lisy@gmail.com>:
On 3/1/17, Steven D'Aprano <steve@pearwood.info> 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 Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/