[Python-ideas] YAML (yet-another-multiline-lambda)

[Andrew Barnert]

On Oct 22, 2013, at 11:07, Steven D'Aprano <steve at pearwood.info> wrote:

> On Tue, Oct 22, 2013 at 09:27:59AM -0700, Andrew Barnert wrote:
>> On Oct 22, 2013, at 5:39, Steven D'Aprano <steve at pearwood.info> wrote:
>> 
>>> On Tue, Oct 22, 2013 at 03:10:29AM -0700, Antony Lee wrote:
>>> 
>>>> Specifically, I suggest that the "def" (and possibly the "class")
>>>> keyword(s) may be used in an expression context, if immediately surrounded
>>>> by parentheses.  
>>> 
>>> I don't think there is any need to allow class in an expression, since 
>>> we already have type().
>> 
>> But type doesn't allow you to do most of what you can do in a class definition. This is like arguing that we don't need expression def because we already have types.FunctionType.
> 
> Given multi-line lambda, what could you do in a class definition that 
> you couldn't do with type?

Write code that's somewhat readable and looks somewhat like Python?

> class Spam(SpamBase, HamBase):
>    x = 1
>    def eggs(self, arg):
>        return arg+self.x
> 
> classes = [int, str, Spam, float]
> 
> 
> would become:
> 
> 
> classes = [int, str, 
>           type('Spam', (SpamBase, HamBase), 
>                {'x': 1, 
>                 'eggs': (def eggs(self, arg):
>                              return arg+self.x
>                              ),
>                }
>               ),
>           float,
>           ]
> 
> 
> which I personally don't consider an improvement, but some people might. 

Anyone who finds that an improvement clearly would rather be using a different language than python in the first place.

> You could even handle metaclasses and extra arguments:
> 
> class Spam(SpamBase, metaclass=MetaSpam, extrakw="extra"):
>    ...
> 
> becomes:
> 
> MetaSpam('Spam', (SpamBase,), {...}, extrakw="extra")
> 
> so given a def expression, I don't think we also need a class 
> expression. What's missing?
> 
> 
> 
> -- 
> Steven
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