[Python-ideas] The way decorators are parsng

[Eric Snow]

On Wed, Oct 19, 2011 at 3:43 PM, Chris Rebert <pyideas at rebertia.com> wrote:
>> On Wed, Oct 19, 2011 at 2:32 PM, Tarek Ziadé <ziade.tarek at gmail.com> wrote:
>> Hello
>>
>> Today I've tried to write a one-liner for a decorator, The decorator
>> is a method in a class.
>>
>> I wanted to do something like this:
>>
>> @Class().decorator()
>> def function():
>>    ...
>>
>> That threw a syntax error to my surprise.
> <snip>
>> Is there something obvious I am missing, or is there a weird thing in
>> the way decoratirs are parsed ?
>
> PEP 318 -- Decorators for Functions and Methods
> (http://www.python.org/dev/peps/pep-0318/ ):
> "Current Syntax
> [...]
> The decorator statement is limited in what it can accept -- arbitrary
> expressions will not work. Guido preferred this because of a gut
> feeling [17]."
> [17]: http://mail.python.org/pipermail/python-dev/2004-August/046711.html
>
> According to Python 2.7's grammar
> (http://docs.python.org/reference/grammar.html ):
>    decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE
>    dotted_name: NAME ('.' NAME)*
>
> So, you're limited to an arbitrarily-long sequence of attribute
> accesses, followed by an optional call.

Interesting.  I would have expected at least the following to work:

    decorator: '@' NAME trailer* NEWLINE
    trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME

Regardless, good to know, even if uncommon.

-eric

>
> Cheers,
> Chris
> --
> http://rebertia.com
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