< is the strict subset operator. <= is subset. What more can I say? On Mon, Mar 23, 2020 at 02:01 Steven D'Aprano <st...@pearwood.info> wrote:
> On Sun, Mar 22, 2020 at 09:49:26PM -0700, Guido van Rossum wrote: > > On Sun, Mar 22, 2020 at 6:51 PM Steven D'Aprano <st...@pearwood.info> > wrote: > > > > > We might have a terminology issue here, since according to Wikipedia > > > there is some dispute over whether or not to include the equality case > > > in subset/superset: > > > > > > https://en.wikipedia.org/wiki/Subset > > > > > > For what it is worth, I'm in the school that subset implies proper > subset > > > [...] > > > > > > > Wikipedia's pedantry notwithstanding, I don't think this is a useful > > position *when talking about Python sets*, since Python's set's > .issubset() > > method returns True when the argument is the same set: > > But Python's subset *operator* returns False when the arguments are > equal: > > py> {1} < {1} > False > > and until today I did not realise the operator and method used different > definitions. I'm going to have to review some of my code using sets to > see if my mistaken understanding that they were the same has introduced > some hidden bugs :-( > > I'm not going to get into an argument about which definition is correct. > I think the differences between the operators and the methods should be > better described in the docs, but at least the docs do explicitly note > that set.issubset is equivalent to the `<=` operator. > > (Not the docstring though. You have to read the docs on the website.) > > Today I read Wikipedia's pedantry and learned for the first time that > there are people who define "subset" to include equality. I had not come > across that before, so I was confused by Steve Jorgensen's talk about > sets that are similtaneously subsets and supersets of themselves. But > now that I realise he is talking about *equal* sets, it makes sense. > > I'm still confused by his position that there are sets (iterables?) > which are simultaneously subsets and supersets of each other without > being equal, but that's a separate issue for him to clarify. > > > -- > Steven > _______________________________________________ > 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/4CAPJG2EEAYPDQWXJ5PVBXNUZ7GWULER/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido (mobile)
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