On Thu, Oct 13, 2016 at 6:55 PM, Steven D'Aprano <st...@pearwood.info> wrote:
> On Thu, Oct 13, 2016 at 04:34:49PM +0200, Martti Kühne wrote:
>
>> > If I had seen a list comprehension with an unpacked loop variable:
>> >
>> > [t for t in [(1, 'a'), (2, 'b'), (3, 'c')]]
>
> Martti, somehow you have lost the leading * when quoting me. What I
> actually wrote was:
>
> [*t for t in [(1, 'a'), (2, 'b'), (3, 'c')]]
>
Sorry for misquoting you. Can I fix my name, though?
Also, this mail was too long in my outbox so the context was lost on it.
I reiterate it, risking that I would annoy some, but to be absolutely clear.
>
>> As it happens, python does have an external consumption operation that
>> happens externally with an iteration implied:
>>
>
> If you replace the t with *t, you get a syntax error:
>
I meant that statement in context of the examples which were brought up:
the occurrence of a list comprehension inside an array have the
following effect:
1) [ ..., [expr for t in iterable] ]
is equivalent to:
def expr_long(iterable, result):
result.append(iterable)
return result
expr_long(iterable, [ ..., ])
so, if you make the case for pep448, you might arrive at the following:
2) [ ..., *[expr for expr in iterable] ]
which would be, if I'm typing it correctly, equivalent to, what
resembles an external collection:
def expr_star(list_comp, result):
result.extend(list(list_comp))
return result
expr_star(iterable, [ ..., ])
Having this in mind, the step to making:
[ ..., [*expr for expr in iterable], ]
from:
def expr_insidestar(iterable, result):
for expr in iterable:
result.extend(expr)
return result
does not appear particularly far-fetched, at least not to me and a few
people on this list.
cheers!
mar77i
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