I can't promise a patch is accepted before I see it. :-) But the idea is sound, so don't worry about it being rejected on the basis of being an undesirable feature.
--Guido On Jan 22, 2008 12:36 PM, tomer filiba <[EMAIL PROTECTED]> wrote: > i can work on a patch, but before i start, i want to make sure it's > accepted. the change will require sq_contains to return a PyObject, > as well as some minor tweaks to cmp_outcome(). > > > -tomer > > ---------- Forwarded message ---------- > From: Guido van Rossum <[EMAIL PROTECTED]> > Date: Jan 22, 2008 9:55 PM > Subject: Re: [Python-Dev] misbehaving __contains__ > To: tomer filiba <[EMAIL PROTECTED]> > Cc: [EMAIL PROTECTED] > > > The issue is that the sq_contains slot is defined as returning an int, > while the tp_richcompare slot is defined as returning a PyObject *. > > Your first opportunity for changing this will be Py3k. Please submit a patch! > > > > On Jan 22, 2008 11:26 AM, tomer filiba <[EMAIL PROTECTED]> wrote: > > i'm using python to create expression objects, for more intuitive > > usage as > > predicates, for instance: > > x = (Arg(0) > 17) & (Arg(1).foo == "bar") > > instead of > > x = And(Gt(Arg(0), 17), Eq(GetAttr(Arg(1), "foo"), "bar")) > > > > so now i can use x.eval(18, "spam") and get the result of the > > expression. > > > > i'm doing it by overriding all the operators to return expression > > objects, instead of evaluating the result immediately. it works > > fine, but i encountered a problem with making > > __contains__ behave so. > > > > it turns out __contains__ coerces the return value into a bool. > > this might seem logical at first, but is not consistent with > > the rest of the language. > > > > consider the following code: > > > > >>> class Foo(object): > > ... def __contains__(self, key): > > ... return 17 > > ... def __eq__(self, other): > > ... return 19 > > ... > > >>> > > >>> f=Foo() > > >>> f == 8 > > 19 > > >>> 8 in f > > True > > > > as you can see, __eq__ does not coerces the result to bool, so why > > should __contains__ do that? > > > > i've looked at PySequence_Contains in objects/abstract.c, but i can't > > quite understand where the coercion is made. is because the > > function is typed as int? if so, i believe it should either be > > changed to PyObject, or have cmp_outcome (in ceval.c) not use this > > API directly, and rather return the result, as it is returned > > from __contains__. > > > > i see no reason it should behave differently than __eq__ and the rest > > of comparison operators. > > > > > > -tomer > > -- > > --Guido van Rossum (home page: http://www.python.org/~guido/) > -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
