On Jan 7, 2008 8:48 PM, hashcollision <[EMAIL PROTECTED]> wrote: > > > > But the biggest thing missing is precise semantics. Saying "exactly > > the same semantics as with Python 2.5" doesn't cut it (those semantics > > are incredibly hairy and sometimes surprising, and their > > implementation was a nightmare -- I've rarely been as relieved as when > > I was able to cut those out of the implementation). > > > Why is that so? I might be being naive, but what is wrong with something > like this: > > def cmp(a, b): > if hasattr(a, '__cmp__'): > return a.__cmp__(b) > elif hasattr(b, '__cmp__'): > return -1 * b.__cmp__(a) > elif hasattr(a, '__le__') and hasattr(a, '__ge__'): > x = a <= b > y = a >= b > if x and y: > return 0 > elif x: > return -1 > elif y: > return 1 > elif hasattr(b, '__le__') and hasattr(b, '__ge__'): > x = b <= a > y = b >= a > if x and y: > return 0 > elif x: > return 1 > elif y: > return -1 > elif hasattr(a, '__eq__'): > if a == b: > return 0 > if hasattr(a, '__lt__'): > if a < b: > return -1 > else: > return 1 > elif hasattr(a, '__gt__'): > if a > b: > return 1 > else: > return -1 > else: > raise NotImplemented() > elif hasattr(b, '__eq__'): > if a == b: > return 0 > if hasattr(b, '__lt__'): > if b < a: > return 1 > else: > return -1 > elif hasattr(b, '__gt__'): > if b > a: > return -1 > else: > return 1 > else: > raise NotImplemented() > else: > raise NotImplemented()
You don't call that hairy? :-) Anyway, one of the additional complications is that it is supposed to be implemented in C, and there is one C slot for all six comparisons together (which of the six is an argument). The 2.x rules are also further complicated in that sometimes the RHS is tried before the LHS (in case the RHS is an instance of a subclass of the class of the LHS). And I think you've ignored the possibility that a.__cmp__(b) might return NotImplemented. Just believe me, it's hairy. -- --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
