[Python-ideas] Syntax for passing lambdas to functions

[Haoyi Li]

> Please admit that this is way, way prettier.

If it's just a matter of prettyness, why not just alias lambda as λ

Then we can have

matrix.transform(λ x, y: (y, x))

I think it looks way prettier than either one: it doesn't have the
verbosity of the lambda version, and doesn't have the weird contextuality
of the = version.



On Thu, Feb 27, 2014 at 3:38 PM, Joshua Landau <joshua at landau.ws> wrote:

> On 27 February 2014 04:19, Steven D'Aprano <steve at pearwood.info> wrote:
> > On Wed, Feb 26, 2014 at 11:44:51AM -0800, Andrew Barnert wrote:
> >
> >> But it becomes more useful if you do anything else:
> >>
> >>     Button("Do it!", on_click() = fire_the_ducks(42))
> >>
> >>
> >> At first glance, I think this is nice,
> >
> > At first glance, it looks like you are setting the on_click argument to
> > the result of fire_the_ducks(42). This proposed syntax is going to be
> > *really easy* for people to misinterpret when they see it in use. And
> > not just novices -- I think this will be syntax that just begs to be
> > misinterpreted when reading code, and misused when writing it.
> >
> > I think that having special syntax for anonymous function only inside
> > function calls with keyword arguments is a violation of the Zen of
> > Python (see the one about special cases) and the Principle Of Least
> > Surprise. It's really a bad idea to have syntax for a "shorter lambda"
> > that works here:
> >
> >     f(arg=***whatever***)
> >
> > but not in these:
> >
> >     f(***whatever***)
> >     [len, zip, map, ***whatever***, some_function]
> >     result = ***whatever***(arg)
>
> I don't follow. I know it's different, but we have
>
>     f(*args) but not [*args]
>
> And we have
>
>     start, *mid, end = [1, 2, 3] but not (lambda start, *mid, end: ...)(1,
> 2, 3)
>
> and we have
>
>     (lambda x: ...)(*[...]) but not foo = *[...]
>
> ... *wink¹*
>
> It's not silly to think that things are context-sensitive in a
> context-sensitive language. Personally this proposal makes sense and I
> honestly don't see the confusion that's being stated. It makes things
> significantly prettier and more readable, for one.
>
> Further, for consistency one can define:
>
>     matrix.transform((x, y)=(y, x))
>
> as an "anonymous" version, compiling to
>
>     matrix.transform(lambda x, y: (y, x))
>
> Please admit that this is way, way prettier.
>
> PS: One problem. "f( (a) = ... )" is currently valid. So is "f(
> (((((a))))) = ... )". Why the hell is this so? "(a) = 2" is valid, but
> so is "(a, b) = (2, 3)", whereas "f( (a, b) = (2, 3) )" is not.
>
> ¹http://www.python.org/dev/peps/pep-0448/
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