[Python-Dev] method decorators (PEP 318) (original) (raw)

Alex Martelli aleaxit at yahoo.com
Sat Mar 27 14:47:44 EST 2004

On 2004 Mar 27, at 19:11, Skip Montanaro wrote:

Barry> attributes, but decorators can also do the trick in a nasty way: Barry> Barry> def foobar [ Barry> lambda f: f.author = 'Guido van Rossum', Barry> lambda f: f.deprecated = True, Barry> classmethod] (self, arg): Barry> # Now what?

Alex> Not necessarily all that nasty: Alex> def foobar [ withattributes( Alex> author="Guido van Rossum", Alex> deprecated=True), Alex> classmethod] (cls, args): Alex> pass Both cases demonstrate why I don't like the decorator-before-args option. Where are the args? Like I said in an earlier post most of the time I look at a function def wanting a quick reminder how to call it. If the argument list doesn't at least start on the same line as the def I think that will be tougher.

As long as the decorators don't come between the def and the function name (that WOULD be far too early and impede looking for 'def foo' to easily locate the definition) I'll be OK, but, sure, I do agree that right before the colon is the best place for the decorators. I was just using the same hypothetical syntax as Barry was using in his own snippet.

Alex> with a built-in 'withattributes' equivalent to:

Alex> def withattributes(f, **kwds): Alex> for k, v in kwds.iteritems(): Alex> setattr(f, k, v) Alex> return f Not quite. It has to be written as a function which returns another function, e.g.: def attrs(**kwds): def decorate(f): f.dict.update(kwds) return f return decorate

Yes, you're right, this is what the semantics must be (assuming that "setattr(f, n, v)" does absolutely nothing more than "f.dict [n] = v", a hypothesis I wasn't ready to make -- I'm not sure it's currently guaranteed by the language reference manual -- but if I'm wrong and it IS so guaranteed and I just missed the spot thus guaranteeing, the bulk update is of course a speedier approach than the loop I had).

Alex

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