On Mon, Jan 8, 2018 at 11:35 AM, Ben Finney via Python-list <python-list@python.org> wrote: > Chris Angelico <ros...@gmail.com> writes: > >> On Mon, Jan 8, 2018 at 10:55 AM, Ben Finney <ben+pyt...@benfinney.id.au> >> wrote: >> > We've established that it is useful to allow data types to define >> > their own meaning of “equal” and “not equal”, like many other >> > operations. Is that not good enough reason to allow it still? >> >> The fact that container types can define "contains" but can't define >> "doesn't contain", and that (as of Py3) there's proper default >> handling, suggests that it's not as big a priority now. > > That is an inconsistency, I agree. > >> Let's put it this way. Suppose that __eq__ existed and __ne__ didn't, >> just like with __contains__. Go ahead: sell the notion of __ne__. >> Pitch it, show why we absolutely need to allow this. > > I think “reject unless absolutely needed” is an unreasonably high bar, > which would disqualify most Python language features. So I don't know > why you expect this to be so especially strongly argued.
True, I exaggerated a bit. But do you think that, had __ne__ not existed for years, its addition could be justified? >> Make sure you mention the potential confusion when subclassing. > > For example, that would alsop be a problem for multiple inheritance. Not > “absolutely needed”, and high risk of confusion when subclassing. Do you > think that multiple inheritance would thereby also not be allowed today? > > If you consider that a different case, why? There's a LOT that you can do usefully with MI that you can't do without it. Having spent a few years (many years ago) working with Java, I appreciate the ability to inherit from more than one class. Does it have to be done the way Python currently does it? No. But one way or another, it's a massively useful feature. (You're right that "absolutely needed" is too high a bar, but hyperbole aside, I do think that MI hits a higher mark than __ne__ does.) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
