Steven D'Aprano <[EMAIL PROTECTED]> writes: > On Fri, 21 Nov 2008 17:26:21 +0000, Arnaud Delobelle wrote: > > [...] >> As classes can be decorated in Python 3, you can write a decorator to >> make a class totally ordered. Here is a very simplified proof of >> concept such decorator: >> >> def totally_ordered(cls): >> if not hasattr(cls, '__gt__'): >> def gt(self, other): >> return self != other and not self < other >> cls.__gt__ = gt >> # Do the same with __le__, __ge__ >> return cls >> >> >> @totally_ordered >> class Fraction: >> def __init__(self, num, den=1): >> assert den > 0, "denomintator must be > 0" self.num = num >> self.den = den >> def __eq__(self, other): >> return self.num*other.den == self.den*other.num >> def __lt__(self, other): >> return self.num*other.den < self.den*other.num >> >>>>> q12=Fraction(1, 2) >>>>> q23=Fraction(2, 3) >>>>> q12 < q23 >> True >>>>> q12 > q23 >> False >> >> Granted it's not as efficient as a __cmp__ function. > > What makes you say that? What do you mean by "efficient"? Are you talking > about memory footprint, runtime speed, disk-space, programmer efficiency, > algorithmic complexity, or something else?
What I'm talking about is very simple - and explained below, with the help of your __cmp__ method. > > As I see it, a __cmp__ method would be written something like this: > > def __cmp__(self, other): > return cmp(self.num*other.den, self.den*other.num) I'm talking about runtime speed (*not* asymptotic complexity). My code makes Fraction.__gt__ about twice as slow as Fraction.__lt__ or Fraction.__eq__ even though with __cmp__ they would all be equally fast. -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
