On Sat, 16 Oct 2021, David Mertz, Ph.D. wrote:
On Sat, Oct 16, 2021, 10:10 AM Erik Demaine
(*it1, *it2, *it3) # tuple with the concatenation of three
iterables
[*it1, *it2, *it3] # list with the concatenation of three
iterables
{*it1, *it2, *it3} # set with the union of three iterables
{**dict1, **dict2, **dict3} # dict with the combination of
three dicts
I'm +0 on the last three of these.
But the first one is much more suggestive of a generator comprehension. I
would want/expect it to be equivalent to itertools.chain(), not create a
tuple.
I guess you were referring to `(*it for it in its)` (proposed notation) rather
than `(*it1, *it2, *it3)` (which already exists and builds a tuple).
Very good point! This is confusing. I could also read `(*it for it in its)`
as wanting to build the following generator (or something like it):
```
def generate():
for it in its:
yield from it
```
I guess the question is whether to define `(*it for it in its)` to mean tuple
or generator comprehension or nothing at all. Tuples are nice because they
mirror `(*it1, *it2, *it3)` but bad for the reasons you raise:
Moreover, it is an anti-pattern to create large and indefinite sized tuples,
whereas such large collections as lists, sets, and dicts are common and
useful.
I'd be inclined to not define `(*it for it in its)`, given the ambiguity.
Assuming the support remains relatively unanimous for [*...], {*...}, and
{**...} (thanks for all the quick replies!), I'll put together a PEP.
On Sat, 16 Oct 2021, Guido van Rossum wrote:
Seems sensible to me. I’d write the equivalency as
for x in y: answer.extend([…x…])
Oh, nice! That indeed works in all cases.
Erik
--
Erik Demaine | edema...@mit.edu | http://erikdemaine.org/
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