This stems from a query on StackOverflow: https://stackoverflow.com/questions/47272460/python-tuple-unpacking-in-return-statement/

Specifically, the following syntax is allowed:
def f():
    rest = (4, 5, 6)
    t = 1, 2, 3, *rest

While the following result in SyntaxError:
def g():
    rest = (4, 5, 6)
    return 1, 2, 3, *rest

def h():
    rest = (4, 5, 6)
    yield 1, 2, 3, *rest

Looking at the original commit that enabled tuple unpacking in assignment statements:
https://github.com/python/cpython/commit/4905e80c3d2f6abb613d212f0313d1dfe09475dc

I don't believe this difference is intentional.

My GitHub repo incorporates a fix for this; I'll file a pull request momentarily.

Since this changes the grammar, it should be first discussed on Python-Dev and approved by BDFL.

CLA processed, and BDFL has assented on python-dev. Serhiy, thoughts on next steps?

I think the language spec needs updating as well? In particular in

https://docs.python.org/3/reference/simple_stmts.html#the-return-statement

it seems expression_list should be replaced by starred_list.

Hm... that leaves the only production for expression_list as:
subscription ::= primary "[" expression_list "]"

And I'm not sure that this shouldn't also be replaced by starred_list. It's not accepted today, though:

In [6]: a[1,*(4, 5, 6)]
  File "<ipython-input-6-ba56159162e9>", line 1
    a[1,*(4, 5, 6)]
        ^
SyntaxError: invalid syntax

I will ask about this again on python-dev@

Oops, I wasn't looking broadly enough. This is also used in the augmented assignment statements syntax, e.g. a += 1, 2, 3

Move to 3.8.

BFDL approval: https://mail.python.org/pipermail/python-dev/2017-November/150842.html

Jordan, what's your GitHub account name? I hope you can check this out and make the changes I'm requesting on GitHub.

Here's my GitHub account: I'll make the changes and rebase as soon as I get home.

Sorry, I could have sworn that I pasted my link... https://github.com/jChapman

New changeset fd97d1f1af910a6222ea12aec42c456b64f9aee4 by Guido van Rossum (David Cuthbert) in branch 'master':
bpo-32117: Allow tuple unpacking in return and yield statements (gh-4509)
https://github.com/python/cpython/commit/fd97d1f1af910a6222ea12aec42c456b64f9aee4

Fixed by https://github.com/python/cpython/pull/4509.

New changeset 8fabae3b00b2ccffd9f7bf4736734ae584ac5829 by Miss Islington (bot) (jChapman) in branch 'master':
bpo-32117: Iterable unpacking in return and yield documentation (GH-9487)
https://github.com/python/cpython/commit/8fabae3b00b2ccffd9f7bf4736734ae584ac5829

assertEquals() is deprecated, use assertEqual() instead. This causes tests failure when run with -Werror.

New changeset 4642d5f59828e774585e9895b538b24d71b9df8e by Serhiy Storchaka in branch 'master':
Use assertEqual() instead of assertEquals(). (GH-9721)
https://github.com/python/cpython/commit/4642d5f59828e774585e9895b538b24d71b9df8e

New changeset 627f7012353411590434a7d5777ddcbcc8d97fcd by Javier Buzzi in branch 'master':
bpo-32117: Updated Simpsons names in docs (GH-19737)
https://github.com/python/cpython/commit/627f7012353411590434a7d5777ddcbcc8d97fcd