----- Original Message -----
> From: "Jim Bosch" <tallji...@gmail.com>
> To: "Development of Python/C++ integration" <cplusplus-sig@python.org>
> Sent: Thursday, February 6, 2014 2:51:59 PM
> Subject: Re: [C++-sig] returning list of class pointers that compare equal
>
> On Thu, Feb 6, 2014 at 2:43 PM, Gary Oberbrunner <ga...@genarts.com>
> wrote:
> > ----- Original Message -----
> >> From: "Jim Bosch" <tallji...@gmail.com>
> > ...
> >> - Add a __eq__/__ne__ overrides to the class of things you're
> >> putting
> >> in the list, with an implementation that compares C++ pointers,
> >> not
> >> Python pointers. This is almost certainly much easier, but it's a
> >> little less "complete" as a solution, in the sense that you'll
> >> still
> >> be getting different Python objects back for the same C++ object
> >> (so
> >> while "param2 == param1" will succeed, "param1 is param2" will
> >> still
> >> fail).
> >
> > This is very helpful! That's OK about "is" not working, I think
> > (though true, a little odd.)
> >
> > Can I override __hash__ too, so set membership works correctly?
> > Also do I need to override __ne__; I think not?
> >
> > For the record, here's what I did. Defined a comparison function:
> >
> > static bool params_equal(Param &left, Param &right)
> > {
> > return &left == &right;
> > }
> >
> > and then in the exposer:
> >
> > Param_exposer.def("__eq__", ¶ms_equal);
>
> That should be fine, as long as you don't care about what happens
> when
> you try to compare a Param to something else entirely (idiomatic
> Python behavior would be to return False; this implementation will
> likely raise an exception).
I thought about that; for some reason the above works (no exception). It never
calls my params_equal code; it must have some kind of fallback.
> You should be able to override __hash__ in much the same way, and I'd
> recommend checking to see if __ne__ works as expected before assuming
> you don't need to implement it yourself; I don't recall Python's
> behavior in this case, but I think it has a tendency not to define
> most operators implicitly.
Just tested it, and as you suspect, indeed I do need __ne__, otherwise param1
!= param2 returns True when it should return False.
--
Gary Oberbrunner
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