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

Samuele Pedroni pedronis at bluewin.ch
Wed Sep 1 14:00:41 CEST 2004

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

More information about the Python-Dev mailing list