On 19 Mar 2010, at 03:43, Scott Dial <scott+python- ideas@scottdial.com> wrote:
On 3/18/2010 10:33 PM, Fred Drake wrote:
On Thu, Mar 18, 2010 at 10:28 PM, David Stanek <dstanek@dstanek.com> wrote:
I don't remember seeing much code using function properties. I would probably just create a new decorator for this.
I've not either, but if we determine that this is a useful facility to include in the standard library, I'd be in favor of something like this:
@setattr(printable=True) def f(): """Example function"""
For the sake of a head count, I have used function attributes for the purpose of memoizing computations (both return values and intermediate calculations). A representative example:
@setattr(primes=set(), composites=set()) def is_prime(n): if n <= 0: raise ValueError(n) elif n == 1: return True elif n in is_prime.primes: return True elif n in is_prime.composites: return False for p in is_prime.primes: if n % p == 0: is_prime.composites.add(n) return False is_prime.primes.add(n) return True
But honestly, the biggest problem I have with this pattern is that you explicitly have to say the name of the function since there is no "self" equivalent. I think it would be more maintenance-friendly to do:
def _(n): primes = set() composites = set() def is_prime(n): if n <= 0: raise ValueError(n) elif n == 1: return True elif n in primes: return True elif n in composites: return False for p in primes: if n % p == 0: composites.add(n) return False primes.add(n) return True return is_prime is_prime = _()
Which is to say, I would be more amenable to adding such a feature if it was building closure. And in that usage, it would seem to be more generally useful and well-behaved.. outsiders don't normally modify closures (if you want this sort of interface, you probably should define a class).. it allows you to avoid naming the function in the function.. and it is a much closer substitute for the default arguments kludge that is so commonly abused.
@closure(primes=set(), composites=set()) def is_prime(n): if n <= 0: raise ValueError(n) elif n == 1: return True elif n in primes: return True elif n in composites: return False for p in primes: if n % p == 0: composites.add(n) return False primes.add(n) return True
But, that's just my two cents.
-- Scott Dial scott@scottdial.com scodial@cs.indiana.edu _______________________________________________ Python-ideas mailing list Python-ideas@python.org http://mail.python.org/mailman/listinfo/python-ideas
Why not just use default arguments? Arnaud