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

[Steven D'Aprano]

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?

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. 
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