[Python-Dev] Re: Decorator order implemented backwards? (original) (raw)

Mark Russell marktrussell at btopenworld.com
Sun Aug 15 21:46:03 CEST 2004

On Sun, 2004-08-15 at 18:11, David Eppstein wrote:

It would probably be bad style to have any order dependencies in the evalname evalargs makedec parts, but Brett's order makes more sense to me. That is, I like the actual application of decorators to be in nested order, but it makes more sense to me for the lines constructing the decorators to be evaluated in the order they appear in the code.

On second thoughts I think you are right. I was concerned about the difficulty of explaining the two different evaluation orders, but that is outweighed by the non-intuitiveness of having decorator expressions evaluated in the opposite of source code order. I've updated the patch.

Here's my current attempt at describing the semantics in the reference manual:

A function definition may be wrapped by one or more decorator
expressions. Decorator expressions are evaluated when the function
is defined, in the scope that contains the function definition.
The result must be a callable, which is invoked with the function
object as the only argument.  The returned value is bound to the
function name instead of the function object.  Multiple decorators
are applied in nested fashion.  For example, the following code:

@f1(arg)
@f2
def func(): pass

is equivalent to:

def func(): pass
func = f1(arg)(f2(func))

Mark

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