On Mon, Apr 30, 2018 at 5:55 AM, Tim Peters <tim.pet...@gmail.com> wrote:
> [Tim]
>>> Then `c` is 12, but `a` is still 1 and `b` is still 2. Same thing in the
>>> end:
>>>
>>> c = local(a=3, b=4, a*b)
>
> [Nikolaus Rath <nikol...@rath.org>]
>> I think this can be done already with slighly different syntax:
>>
>> c = (lambda a=3, b=4: a*b)()
>>
>> The trailing () is a little ugly, but the semantics are much more
>> obvious.
>
> But also broken, in a way that can't be sanely fixed. Covered before
> in other messages. Short course:
>
>>>> a = 10
>>>> b = 20
>>>> (lambda a=3, b=a+1: (a, b))()
> (3, 11)
>
> This context really demands (3, 4) instead. In Scheme terms, Python's
> lambda default arguments do "let" binding ("all at once"), but "let*"
> binding is what's needed ("one at a time, left to right, with bindings
> already done visible to later bindings").
So maybe the effective semantics should be:
>>> (lambda a=3: (lambda b=a+1: (a, b))())()
(3, 4)
ChrisA
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