[Python-Dev] @ character choice and Jython (was: Rejecting the J2 decorators proposal)

[Samuele Pedroni]

Guido van Rossum wrote:

> So, what's next? In Python 2.4a3 (to be released this Thursday),
> everything remains as currently in CVS. For 2.4b1, I will consider a
> change of @ to some other single character, even though I think that @
> has the advantage of being the same character used by a similar
> feature in Java. It's been argued that it's not quite the same, since
> @ in Java is used for attributes that don't change semantics. But
> Python's dynamic nature makes that its syntactic elements never mean
> quite the same thing as similar constructs in other languages, and
> there is definitely significant overlap.

One issue with the '@' character choice is that in the context of
Jython things can get rather confusing and I mean beyond the fact
that the need of an "annotation" to get a static method will seem
rather bizarre to Java people. It somewhat put the burden on Jython to 
try to do the obvious thing:

Consider this java annotation definition (concretely these get compiled 
to interfaces):

public @interface Author {
     String value() default "";
}

Now this potential Jython code:

import Author

classs A: # not inheriting from a Java class

   # this also the exact legal java syntax for this
   @Author("batman")
   def method(self):
      pass

in the past and at the moment interfaces are not callable, but here
we would like to produce a nice error or warning, we are not inheriting
from a java class so there is no way to attach the annotation.

But in this case:

import java
import Author

classs A(java.lang.Runnable):

   @Author("batman")
   def run(self): # this one
      pass

here we potentially could attach the annotation to the exposed method.

My point is basically that '@' will likely generate more user questions 
(which are time consuming) and expectations than a different character 
choice in Jython context.

Samuele