[Python-Dev] 2.4a2, and @decorators

[James Y Knight]

On Aug 2, 2004, at 12:55 PM, Phillip J. Eby wrote:
> I would think the fact that the '[decorators]' syntax can be 
> implemented in pure Python (no changes to the interpreter) for 
> existing Python versions would give more weight to it.  That is, if 
> someone wants to implement a decorator that's forwards and 
> backwards-compatible, that's possible with the list syntax, but not 
> the @ syntax.

First off, let me just say I'm happy *one* proposal was selected for 
inclusion. The @foo on the line before the function was not my 
favorite, but that's okay. It'll definitely work.

However, I do think [decorator...] on the line before the function 
definition would be a far worse choice than @decorator. Decorators 
*are* special new syntax. At least @foo *looks* like new syntax. 
[decorators] looks like a expression creating a list, but instead is 
completely magical. Magical syntax seems very poor to me.

About the only advantage it has is that you can implement it via a 
completely horrible hack in Python < 2.4. But, that is only a temporary 
situation. In a few years everyone will have Python >= 2.4 and we'd 
still be stuck with strange weird syntax that doesn't look like syntax.

The one thing I do dislike about the new addition is the arbitrary (?) 
restriction on expression allowed in a decorator. From Grammar..
   decorator: '@' dotted_name [ '(' [arglist] ')' ]
That seems quite odd to me. Is there some reason it couldn't be:
   decorator: '@' test
?

I don't see how that would cause a problem, but maybe I've missed 
something.


Just testing out how this syntax looks, you can ignore the rest of this 
mail. :)

   @classmethod
   @arguments(string, int)
   @returns(list)
   def foo(s, i):
     return [s]*i

or perhaps the same, but with a list allowed:
   @classmethod, arguments(string, int), returns(list)
   def foo(s, i):
     return [s]*i

or original proposal:
   def foo(s, i) [classmethod, arguments(string, int), returns(list)]:
     return [s]*i

Ah well, they all have their advantages. :) This one is workable.

James