On 15.10.2016 16:47, Martti Kühne wrote:
[var for expression in iterable for var in expression]
you are right, though. List comprehensions are already stackable.
TIL.
Good catch, Paul. Comprehensions appear to be a special case when it
comes to unpacking as they provide an alternative path. So, nested
comprehensions seem to unintuitive to those who actually favor the
*-variant. ;) Anyway, I don't think that it's a strong argument against
the proposal. ~10 other ways are available to do what * does and this
kind of argument did not prevent PEP448.
What's more (and which I think is a more important response to the
nested comprehension alternative) is that nested comprehensions are
rarely used, and usually get long quite easily. To be practical here,
let's look at an example I remembered this morning (taken from
real-world code I needed to work with lately):
return [(language, text) for language, text in fulltext_tuples]
That's the minimum comprehension. So, you need to make it longer already
to do **actual** work like filtering or mapping (otherwise, just return
fulltext_tuples). So, we go even longer (and/or less readable):
return [t for t in tuple for tuple in fulltext_tuples if tuple[0] ==
'english']
return chain.from_iterable((language, text) for language, text in
fulltext_tuples if language == 'english'])
I still think the * variant would have its benefits here:
return [*(language, text) for language, text in fulltext_tuples if
language == 'english']
(Why it should be unpacked, you wonder? It's because of executemany of
psycopg2.]
Cheers,
Sven
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