[Python-Dev] PEP 318: Decorators last before colon

Guido van Rossum guido at python.org
Tue Mar 30 17:58:41 EST 2004

> The most obvious issues I see with this is are that:
>   - grepping for "def func" won't show any sign that its decorated, and 

Seems rather minor -- there's only so much you can cram on a single

>   - it looks like normal syntax, so it looks like expressions should
>     work, e.g.
>         [decorator1] + [decorator2]
>         def func(arg, arg):
>     or even:
>         get_std_decorators()   # Returns a list
>         def func(arg, arg):
>     I'm pretty sure this isn't the intention, though.  I can imagine
>     some posts to comp.lang.python asking how to do the above...

The same syntactic restrictions apply to docstrings (you can't have an
expression of type string in the docstring position, it *has* to be a
literal).  Nobody's confused by that one.

> Neither of these are fatal flaws, but I think I still prefer:
>     def func(args) [decorator]:

Which hides 'classmethod' behind the more voluminous stuff, and that's
my main gripe.

My main reasoning is as follows:

1) If we do decorators at all, decorators should be allowed to be
   arbitrary expressions.

2) Since we allow arbitrary expressions, decorators provide a much
   better way to set function attributes than the current way.

3) This will be attractive (better than putting special mark-up in
   docstrings), so there will be lots of voluminous decorators.

4) Then the "important" decorators like classmethod will be hidden at
   the end of the list of decorators.

The [...] prefix proposal addresses this by putting the end of the
decorator list closest to the def keyword.  This doesn't look so bad:

    [funcattr(spark="<spark syntax here>",
    def foo(cls, arg1, arg2):

--Guido van Rossum (home page: http://www.python.org/~guido/)

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