[Python-Dev] Class decorators (original) (raw)

Phillip J. Eby pje at telecommunity.com
Thu Mar 30 02:23:03 CEST 2006

At 11:07 AM 3/29/2006 -0800, Guido van Rossum wrote:

On 3/28/06, Phillip J. Eby <pje at telecommunity.com> wrote: > If we're using Zope 3 as an example, I personally find that: > > class Foo: > """Docstring here, blah blah blah > """ > implements(IFoo) > > is easier to read than: > > @implements(IFoo) > class Foo: > """Docstring here, blah blah blah > """

But the former also smells more of magic.

My comment above was only about readable placement of the decorators, not the actual syntax. Many approaches to the actual syntax in the body are possible.

For example, what did you think of Fred Drakes's "@class" proposal? To specify it formally, one could say that this:

 @class EXPR

in a class scope would expand to the equivalent of:

 locals().setdefault('__decorators__',[]).append(EXPR)

and is a syntax error if placed anywhere else. That, combined with support for processing decorators at class creation time, would fulfill the desired semantics without any implicit "magic".

(The locals() part could of course be implemented in bytecode as LOAD_LOCALS, since class scopes implement their locals as a dictionary. That would avoid the need for adding any new bytecodes, since this isn't a performance-sensitive feature.)

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