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

Guido van Rossum guido at python.org
Fri Mar 26 13:37:58 EST 2004

It's apparent Guido doesn't agree; I just wish I knew what was bothering him about the PEP, so I could either provide a convincing counterargument, or understand better why I'm wrong. <0.5 wink> At the moment, I'm worried that something in my actual use cases will scare him into rejecting the PEP altogether. <0.01 wink>

Let me try to explain what bothers me.

If we were going to use this mostly for decorators spelled with a single work, like classmethod, I would favor a syntax where the decorator(s) are put as early as reasonable in the function definition, in particular, before the argument list. After seeing all the examples, I still worry that this:

def foobar(cls, blooh, blah) [classmethod]:

hides a more important fact for understanding it (classmethod) behind some less important facts (the argument list). I would much rather see this:

def foobar [classmethod] (cls, blooh, blah):

I agree that if this will be used for decorators with long argument lists, putting it in front of the arguments is worse than putting it after, but I find that in that case the current PEP favorite is also ugly:

def foobar (self, blooh, blah) [ metadata(author="GvR", version="1.0", copyright="PSF", ...), deprecated, ]: for bl, oh in blooh: print oh(blah(bl))

I don't see a way to address both separate concerns (hiding the most important fact after the signature, and the ugliness of long complex lists of decorators) with a single syntactic alternative. The two concern are in conflict with each other. That's why I'm trying to pull the proposal apart into two directions: put small decorators in front, put large function attribute sets in the body.

(For those worried that the function attribute sets appear to belong to the body, I point to the precedent of the docstring. IMO the start of the function body is a perfectly fine place for metadata about a function.)

--Guido van Rossum (home page: http://www.python.org/~guido/)

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