[Python-ideas] Another attempt at a sum() alternative: the concatenation protocol

[Oscar Benjamin]

On 16 July 2013 15:48, Masklinn <masklinn at masklinn.net> wrote:
>>> You could wait for PEP 448, which will let you use [*sublist for
>>> sublist in list_to_be_flattened].
>>
>> Well that does look good. How exactly does it unroll? Does the *
>> translate as yield from but without the weird comprehension turning
>> into a generator function behaviour?
>
> For a listcomp, surely it translates into a .extend of the accumulator?

So
    [a for b in c]
is
    for b in c:
        result.append(a)
and
    [*a for b in c]
is
    for b in c:
        result.extend(a)

Set and dict comps presumably use .update. And the generator expression
    (*a for b in c)
becomes
    for b in c:
        for x in a:
            yield x
or is it actually (this is not equivalent):
    for b in c:
       yield from a

Currently,
    ((yield from a) for b in c)
becomes:
    for b in c:
        yield (yield from a)
which is perhaps less useful (because of the additional yielded None values).


Oscar


Oscar