[Python-Dev] Re: Call for defense of @decorators (original) (raw)

Christian Tismer tismer at stackless.com
Sat Aug 7 01:04:22 CEST 2004

Martin v. Löwis wrote:

Christian Tismer wrote:

the primary purpose of all the decorator syntax effort is to get the

foo = classmethod(foo) into the right place, not after but before the definition. Dunno if this was mentioned before, but why not simply do that? Move the statement right before the def and provide a way that this gets recognized correctly. No syntax change, just the convenience people asked for. I don't think this can work. How precisely would you implement it? Python traditionally executes source code from top to bottom, except for loops.

Hey, this is an implementation detail, isn't it? :-)

I can think of a couple of ways to implement it. One would be to defer execution of a statement with undefined names until the end of the whole code block in the case of a class definition and to resolve the names late. Cleaner would probably be to have something like a placeholder for the undefined function, assign to the name a special object and trap the def statement to resolve the object. (this comes to me since I'm just dealing with reference objects in PDF files, which are filled in later).

No, I was really not concerned about how to do this, surely it won't work with plain sequential execution, but other proposals (which Guido considered once) like just putting [decorator] in front of things also needs some (simpler of course) special handling.

At the risk of getting slogged, I also thought of

myfunc := classmethod(myfunc)

for a short time, with ":=" as a late binding assignment operator which defers its operation until myfunc is defined, but I think this is not a popular idea. :-)

To save some typing (laziness was also a driver for this whole decorator nightmare), we could also remove the assignment and just have a function call like

classmethod(myfunc)

which reduces the re-typing to two.

Anyway, compared to the expected effect, this whole discussion appears worse to me than the ternary expression thread last year, where one at least could learn something new. Fine that a?b:c and friends were put down. I really hate to see so much time wasted just for decorators. I could live with a special rule like my little proposal. I also agree that all the syntax pirouettes tried so far just add more ugliness to the language, just for nothing. Using a single char as a prefix might be a compromise after all. But must it be "@", such an eye-catching, ugly piece of flie-dirt? Looks like macro-alert, hey we get into special mode and decorate tokens in special contexts for special meaning. This is even worse than what Prothon tries with ? and !. If @, why not $, this might attract Perl users to Python.

If we are getting perverse, why not simply go and add decorators using XML syntax?

I'd-like-to-ask-green-peace-to-protect-my-language -- chris

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