On 11/25/2017 1:55 AM, David Cuthbert wrote:
First time contributing back -- if I should be filing a PEP or something like
that for this, please let me know.
I don't think a PEP is needed.
Coming from https://bugs.python.org/issue32117, unparenthesized tuple unpacking
is allowed in assignments:
rest = (4, 5, 6)
a = 1, 2, 3, *rest
Because except for (), it is ',', not '()' that makes a tuple a tuple.
but not in yield or return statements (these result in SyntaxErrors):
return 1, 2, 3, *rest
yield 1, 2, 3, *rest
To be crystal clear, a parenthesized tuple with unpacking *is* valid.
return (1, 2, 3, *rest)
yield (1, 2, 3, *rest)
So is an un-parenthesized tuple without unpacking.
Since return and yield are often the first half of a cross-namespace
assignment, requiring the () is a bit surprising. Perhaps someone else
has a good reason for the difference. Otherwise, +1 on the change.
The unpacking in assignments was enabled by a pre-3.2 commit that I haven't yet
been able to track back to a discussion, but I suspect this asymmetry is
unintentional. Here's the original commit:
https://github.com/python/cpython/commit/4905e80c3d2f6abb613d212f0313d1dfe09475dc
I've submitted a patch (CLA is signed and submitted, not yet processed), and
Serihy said that since it changes the grammar I should have it reviewed here
and have signoff by the BDFL.
While I haven't had a need for this myself, it was brought up by a user on
StackOverflow
(https://stackoverflow.com/questions/47272460/python-tuple-unpacking-in-return-statement/47326859).
Thanks!
Dave
--
Terry Jan Reedy
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