On Mon, Jul 7, 2014, at 16:36, Andreas Maier wrote: > Am 2014-07-07 19:43, schrieb Ethan Furman: > > On 07/07/2014 09:56 AM, Andreas Maier wrote: > >> Am 07.07.2014 17:55, schrieb Ethan Furman: > >>> On 07/07/2014 04:22 AM, Andreas Maier wrote: > >>>> > >>>> Where is the discrepancy between the documentation of == and its > >>>> default implementation on object documented? > >>> > >>> There's seems to be no discrepancy (at least, you have not shown it), > >> > >> The documentation states consistently that == tests the equality of > >> the value of an object. The default implementation > >> of == in both 2.x and 3.x tests the object identity. Is that not a > >> discrepancy? > > > > One could say that the value of an object is the object itself. Since > > different objects are different, then they are not equal. > > > >>> but to answer the question about why the default equals operation is an > >>> identity test: > >>> > >>> - all objects should be equal to themselves (there is only one that > >>> isn't, and it's weird) > >> > >> I agree. But that is not a reason to conclude that different objects > >> (as per their identity) should be unequal. Which is > >> what the default implementation does. > > > > Python cannot know which values are important in an equality test, and > > which are not. So it refuses to guess. > > > Well, one could argue that using the address of an object for its value > equality test is pretty close to guessing, considering that given a > sensible definition of value equality, objects of different identity can > very well be equal but will always be considered unequal based on the > address.
Probably the best argument for the behavior is that "x is y" should imply "x == y", which preludes raising an exception. No such invariant is desired for ordering, so default implementations of < and > are not provided in Python 3. _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
