Pre/Postconditions with decorators

[Robert Brewer]

Stephen Thorne wrote:
> On 6 Jan 2005 13:33:42 -0800, Rittersporn 
> <rittersporn at gmail.com> wrote:
> > @condition("number>0 and number<2","result>=0")
> > def sqrt(number):
> >         import math
> >         return math.sqrt(number)
> > 
> > @condition("list(seq) is not None","sum(seq)==result")
> > def my_sum(seq):
> >         tmp=0
> >         for element in seq:
> >                 tmp+=element
> >         return tmp
> > 
> > print sqrt(1.2)
> > print my_sum([1,2,3])
> 
> I think it would be nicer to have the pre and post conditions 
> being compilable.

Me too.

> @condition((list(seq) is not None for seq in args), (sum(seq)==result
> for ((seq,), result) in (args, result))
> 
> or something silly like that.

Ian Bicking was just talking about @require decorators:
http://blog.ianbicking.org/already-under-our-noses.html

@require(int, int)
def gcd(a, b):
    ...

If we made a "checker" module for such things in the stdlib, we could
write most of that:

from checker import *

@args((list, itemsnotNone, ))
@returns((any, ))
def my_sum(seq):
    tmp=0
    for element in seq:
        tmp+=element
    return tmp


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org