[Python-Dev] Questions about '@' in pep 318 (original) (raw)

M.-A. Lemburg mal at egenix.com
Fri Aug 6 13:07:35 CEST 2004

Guido van Rossum wrote:

In essence, you are proposing to reserve a new keyword. Solutions creating new keywords have been ruled out because they might break existing code.

Perhaps this could be addressed by requiring "from future import decorators", for one release, just like was done for "yield". I expect that this would be acceptable to the ObjC folks, too. It wouldn't be my favorite, but I won't rule it out just because of the new keyword (and yes, this is a softening of my position on new keywords).

At EuroPython 2004 I had the impression that folks were not really ready for a finalization on the feature. Your conclusion at the conference was to wait for another release before making a final decision which was well accepted by the audience.

With all the fuzz around this issue, I think that was a wise decision and wonder why "something" now sneaked into 2.4a2.

Not being a big fan of decorative art, I'm a firm -0 on whatever the final syntax may be, but just to throw in an idea from someone who has not participated in all the talk about decorator, here's some food for thought:

"""

  1. Instead of trying to overgeneralize, we only allow exactly one decorator per function definition.

  2. Since decorators change the definition of a function, that one decorator call is placed directly after the "def" and before the function name.

Examples:

def staticcounted(func): return staticmethod(countcalls(func))

class MyClass:

def classmethod test1(selfclass, x):

    """ Test method.
    """
    print x

def staticcounted test2(self, x):

    """ Test method.
    """
    print x

If someone needs more than one decorator or wants to do funky stuff, it's easy enough to define a combining generator for that particular need (see e.g. staticcounted).

The only argument I heard at the conference against placing the decorator between the "def" and the function name was that of losing the "grep'ability" in this case. I don't consider that much of a loss, since it only applies to new code and cases where you actually make use of decorators. The simple nature of the syntax also guarantees that you can easily modify your grep expression to accomodate for possible decorators in front of the name (you'll only ever have one).

"""

If you don't like the idea, that's fine, but perhaps it spurs some new thoughts of how to make this whole decorator thing fit better the elegance of the language.

-- Marc-Andre Lemburg eGenix.com

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