On Fri, Jul 20, 2018 at 4:45 AM, Stephan Houben <stephan...@gmail.com> wrote: > Let me just address this point: > > 2018-07-19 20:36 GMT+02:00 Brendan Barnwell <brenb...@brenbarn.net>: >> >> As far as I can see, these null-coalescing operators would break >> that model. The PEP doesn't seem to provide for a "real" magic method >> allowing users to override the actual behavior of the method. (You can only >> override __has_value__ to hook into it, but not define by fiat what A ?? B >> does, as you can with other operators.) And I think the reason for this is >> that the operator itself is too specific, much more specific in semantics >> than other operators. (I had similar doubts about adding the >> matrix-multiplication operator @.) > > > I think the actual reason is that it is a short-cutting operator, and none > of > the shortcutting operators (and, or, if/else) have an associated method. > They cannot have, since they induce a non-standard evaluation order, > hence their effect cannot be emulated with a method invocation.
Also for the same reason that the 'is' operator doesn't have a corresponding dunder. You can't ask an object if it's the same object as another; it either is or is not, intrinsically. It's the same here; it either is None, or is not None, intrinsically. These new operators have very clearly defined semantics involving the special object None, and they short-circuit; two good reasons NOT to have them overridable. ChrisA _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
