[Python-Dev] def ... decorate

[Roman Suzi]

On Fri, 13 Aug 2004, Skip Montanaro wrote:

>with
>
>    def p_statement_expr:
>        staticmethod
>        grammarrule('statement : expression')
>        version("Added in 2.4")
>        deprecatedmethod
>        type_(None)
>    decorate (self, p):
>        """docstring here"""
>        print p[1]

Bingo!

Just replace decorate with "from" and the nice syntax is found:

    def f:
        staticmethod
        grammarrule('statement : expression')
        version("Added in 2.4")
        deprecatedmethod
        type_(None)
    from self, p:
        """docstring here"""
        print p[1]

 + doesn't surprise Python programmer, because it is like try-except, etc
 + reads a natural language (with implicit "with"  after "f")
 + doesn't require any new keywords or symbols and "prefix" operators
 + is explicit about transformation
 + no additional indentation
 - grepping for defs now require more effort, so probably second name should
   be allowed after "from" or exactly this.

As a variant, docstring could be moved to the upper part.

I'd also liked being able to write:

   def f:
        staticmethod; grammarrule('statement : expression')
        version("Added in 2.4");  deprecatedmethod;  type_(None)
   from x, y:
      pass #...

and:

  def f: staticmethod
  from x, y: return x+y



>It seems different enough from other solutions that I thought it worth
>tossing out.  I didn't see it mentioned in the PythonDecorators moin page.
>
>Read it something like "define a function named p_statement_expr using a
>bunch of functions to decorate the basic function".
>
>It solves a couple problems:
>
>1. "def" introduces the function definition instead of an arbitrary number
>   of @-expressions.
>
>2. There is no extra indentation of the main body.
>
>3. The name of the function is known early on.
>
>4. "def"/"decorate" pair up visually much the same as "try"/"except" or
>   "if"/"then", though they don't represent alternative blocks of code to be
>   executed.
>
>On the minus side it introduces a vertical separation between the function
>name and parameter list and introduces a new keyword, "decorate".
>
>>From a parsing standpoint I think it will work.  You'll see either a colon
>or a left paren after the function name to distinguish between the two types
>of function definition.  I'm not sure if a token needs to be used to
>separate the various decorator functions or if requiring a newline and
>indentation is sufficient.
>
>Skip
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Sincerely yours, Roman Suzi
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