On Dec 6, 1:12 pm, "Diez B. Roggisch" <[EMAIL PROTECTED]> wrote: > samwyse schrieb: > > > For whatever reason, I need an inproved integer. Sounds easy, let's > > just subclass int: > > >>>> class test(int): > > pass > > > Now let's test it: > > >>>> zed=test(0) > >>>> zed.__class__ > > <class '__main__.test'> > >>>> zed > > 0 > > > So far, so good. Now let's try incrementing: > > >>>> zed+=1 > >>>> zed > > 1 > >>>> zed.__class__ > > <type 'int'> > > > WTF??! > > Is this a bug or is it the inevitable result of optimizing for the > > case where all integers are indistinguishable? > > There has been a lengthe thread over the semantics of __iadd__ a few > weeks ago. It _can_ modify the object in question in-place (something > not possible for ints anyway), but it will ALWAYS return a reference > which will be set to the left-hand-side.
Thanks! I'd missed that thread, googling found it but it didn't look noteworthy at first glance. I've not yet read the entire thread, but I did see a reference to PEP 203. ) So, given the expression: ) ) x += y ) ) The object `x' is loaded, then `y' is added to it, and the ) resulting object is stored back in the original place. That agrees with what I'm seeing, all right. The problem is, the resulting object has a different type, which seems to violate the spirit of a later paragraph: ) Writing the above expression as ) ) <x> <operator>= <y> ) ) is both more readable and less error prone, because it is ) instantly obvious to the reader that it is <x> that is being ) changed, and not <x> that is being replaced by something almost, ) but not quite, entirely unlike <x>. And that's my complaint. The value in <zed> is being replaced by something almost, but not quite, identical to the original value. Python's internal implementation of __iadd__ for <int> isn't returning <self>, it's returning a new value belonging to the super-class. My whole point is overloading <int> was that I'd hoped to avoid having to write a bunch of methods to perform in-place modifications. Looks like I stuck, however. -- http://mail.python.org/mailman/listinfo/python-list
