[Python-Dev] @-after-def-before-colon (was Re: def ... decorate)

[Phillip J. Eby]

At 07:52 PM 8/13/04 +0200, Werner Schiendl wrote:

>was the following suggested already? (don't think so):
>
>      def p_statement_expr(self, p):
>          staticmethod
>          grammarrule('statement : expression')
>          version("Added in 2.4")
>          deprecatedmethod
>          type_(None)
>      body:
>          """docstring here"""
>          print p[1]

hmmmm....  that's really not much different from:


    def p_statement_expr(self, p) [
        staticmethod,
        grammarrule('statement : expression'),
        version("Added in 2.4"),
        returns(None)
    ]:
        """Docstring"""
        body

is it?

But then, how about *this*:

    def p_statement_expr(self, p)
        @staticmethod
        @grammarrule('statement : expression')
        @version("Added in 2.4")
        @returns(None)
    as:
        """Docstring"""
        body

The decorators are much more visible with the @ signs.  Also, we could 
possibly allow the docstring to appear in the def statement, rather than in 
the body, e.g.:

    def p_statement_expr(self, p)
        @staticmethod
        @grammarrule('statement : expression')
        @version("Added in 2.4")
        @returns(None)
        """Docstring"""
    as:
        body



Some advantages:

* Tools that just only look at 'def funcname(signature)' still work

* Tools that only look for '@something' at the start of the line will work 
(e.g. I believe this means IPython will still work, dunno about Leo)

* Decorators are much more visible than in the list-after-def forms, but 
are still visibly part of the function definition

* You know the name/signature of the thing being defined before wading 
through decorators


Disadvantages:

* line continuation isn't standard; there ought to be brackets or 
parentheses, otherwise tokenizer will say there's an INDENT, and it's not 
standard to have an INDENT without a colon.

* How would we define the syntax?  Should it be something like this:

   classdef: 'class' NAME ['(' testlist ')'] [decorations] ':' suite
   funcdef: 'def' NAME parameters [decorations] ':' suite

   decorations: NEWLINE INDENT decorator* [docstring NEWLINE] DEDENT 'as'
   decorator: '@' test NEWLINE

In other words, should indent and one-decorator-per-line be enforced?

* Guido has argued that list-after-def is bad in the case of a long 
argument list, because of poor visibility.  Does this approach fix that?