[Python-Dev] PEP 318: Decorators last before colon (original) (raw)

Jewett, Jim J jim.jewett at eds.com
Tue Mar 30 11:34:38 EST 2004

Ka-Ping Yee:

Three different positions for decorators have been suggested:

(a) def [decorator] func(arg, arg): (b) def func [decorator] (arg, arg): (c) def func(arg, arg) [decorator]:

You forgot before and after

using:
    classmethod
def func(arg1, arg2):
    pass

def func(arg1, arg2):
    .classmethod
    pass

There is also a possibility of two separate places, depending on whether the original object is

(1) returned, possibly with extra attributes, or (2) replaced with a new entry point (which might or might not forward to the original, change the signature entirely, do something completely different).

using:
    classmethod
def func(arg1, arg2):
    .annotation
    pass

I would personally prefer to see both types before the def, but separated from each other. I do understand that this gets bulky; it scales up better than it scales down.

note:
    .name1 = value
    .name2 = val2
using:
    classmethod
def func(arg1, arg2):
    pass

There are several strong arguments to choose (c).

1. The decorator part is optional. Optional things usually come at the end and shouldn't interrupt non-optional things.

Agreed, but taking it out of the (current) funcdef header clause entirely also meets this goal. The question is whether it would still bind tightly enough to the funcdef.

4. When you're reading the body of the function, you will refer to the arguments frequently and the decorators not at all. So the arguments should come first, in the usual position.

classmethod does make a difference, because it changes the signature. One of Guido's questions is whether there will ever be a long chain of tranforming decorators.

We have seen examples of long chains of decorators, but I don't think anyone has a concrete use case with more than two transforming decorators. If chains really stay short, then

def classmethod func(arg1, arg2):
    pass

looks OK. (Except that new users will assume classmethod is a keyword, and try to look it up -- which does not work for user-created decorators.)

5. The decorators act on the function after the entire function definition has been evaluated. It makes sense to arrange the function as a visual unit so you can see what is being created and manipulated.

You can already put them after the full definition; the reason for this syntax is to move them up so that people can keep them in mind while reading the definition.

-jJ

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