[Python-Dev] order of decorator application?

[Bob Ippolito]

On Mar 23, 2004, at 12:48 PM, Jewett, Jim J wrote:

> Skip:
>
>> Is there a concensus on the order of application for decorators?
>
> I think people will accept either; the question is what counts as
> "first".
>
> In
> 	name = a(b(c(name)))
>
> Is a first because it appears (and is resolved) first, or is c
> first because it is applied first?
>
> This also interacts with whether the decorators are before or
> after the function name, and with whether we're modelling
>
> 	name = a(name)
> 	name = b(name)
> 	name = c(name)
>
> or
>
> 	name = a(b(c(name)))

I think that the majority opinion is that they should be evaluated left 
to right, which sounds sensible to me because that's how everything 
else works in Python until you start using lots of parentheses.  I 
would probably "accept" either, but I would be very disappointed if it 
wasn't left-to-right.

Either way, if you had a real strong opinion about one direction over 
the other, you could write a function that takes a list of functions 
and applies them in the order you would like them applied, eliminating 
any ambiguity.  The most obvious function to do this would probably 
look something like:

# warning: untested, I don't care if it actually works, it's close 
enough
def left_to_right(*args):
     def left_to_right(fn):
         return reduce(lambda a,b:b(a), args, fn)
     return left_to_right

def decorated()[left_to_right(a, b, c, d)]:
     pass

-bob