[Python-Dev] A grammatical oddity: trailing commas in argument lists.

[Eric Smith]

On 7/9/2010 4:42 PM, Georg Brandl wrote:
> Am 09.07.2010 22:26, schrieb Mark Dickinson:
>> On Fri, Jul 9, 2010 at 8:37 PM, Dino Viehland<dinov at microsoft.com>  wrote:
>>> Terry wrote:
>>>> This violates the important principle that allowed def and call arg
>>>> sequences should match to the extent sensible and possible. In this
>>>> sense, the SyntaxError is a bug. So I would fix this now for 3.2 and
>>>> notify the other implementors.
>>>
>>> +1 on fixing it - trailing commas are awesome.  I'm always annoyed in
>>> C# where I frequently can't use them.  This seems like a bug fix level
>>> change that should be easy for the other implementations to fix.
>>
>> Thanks for all the feedback.
>>
>> If the grammar is changed to allow "def f(*, a,): pass", that still
>> leaves some more open questions:  which of the following should be
>> valid?
>>
>> (1) def f(*args,): pass
>> (2) def f(**kwargs,): pass
>> (3) def f(*,): pass
>
> IMO all of them (though as you mention, (3) doesn't matter.)

Agreed. It's one less thing to explain: "You can have a trailing comma 
in an argument list, unless there's a bare star, and in that case you 
can't have a comma; and also if ...". Ick.

Eric.