Incorrect behavior of the pointer in the form of an upward arrow indicating where the error is on `Invalid star expression`

[vitaldmit]

Bug report

Bug description:

I noticed a strange behavior of the pointer in the form of an upward arrow indicating where the error is.

In 3.10 version there is OK

Python 3.10.12 (main, Feb  4 2025, 14:57:36) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> A[*]
  File "<stdin>", line 1
    A[*]
      ^
SyntaxError: invalid syntax

But in 3.12 and later (sorry there is no 3.11 version on my computer) the up arrow pointer has moved to the right, which is a little confusing.

Python 3.12.2 (main, Feb 15 2024, 13:20:42) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> A[*]
  File "<stdin>", line 1
    A[*]
       ^
SyntaxError: invalid syntax

Same with other expressions:

Python 3.14.0a7+ (heads/main:c46635aa5a2, Apr 29 2025, 21:48:33) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> A[*(1:2)] = 1
  File "<python-input-0>", line 1
    A[*(1:2)] = 1
         ^
SyntaxError: Invalid star expression

More examples in:

del A[*(1:2)]
A[*:]
A[:*]
A[*]
f(**x, *)

and so on...

After this commit (Fix syntax error in handlinh of incorrect star expressions) the error prints as "Invalid star expression", but the pointer in the form of an upward arrow indicating where the error is not point to the star expression. Earlier that commit it's moved to the right.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-133357: Fix SyntaxError carret location on invalid starred exprs #133455
• gh-133357: Add anti-regression test for caret location in error message #133848

[donBarbos]

note: Python 3.11.10 behaves the same as older versions (^ sign to the right of the *)

[sobolevn]

I don't see a big difference in these two example, to be honest:

But, here we can impove

Python 3.14.0a7+ (heads/main:c46635aa5a2, Apr 29 2025, 21:48:33) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> A[*(1:2)] = 1
  File "<python-input-0>", line 1
    A[*(1:2)] = 1
         ^
SyntaxError: Invalid star expression

to be

Python 3.14.0a7+ (heads/main:c46635aa5a2, Apr 29 2025, 21:48:33) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> A[*(1:2)] = 1
  File "<python-input-0>", line 1
    A[*(1:2)] = 1
       ^^^^^
SyntaxError: invalid star expression

CC @lysnikolaou @pablogsal

I can work on this if we agree that this should be done

[terryjreedy]

Starred expressions in subscriptions became possible in 3.11. So in 3.10, the * is invalid and syntax checking stops there. In 3.11, syntax checking continues to look for a valid * expression. But the null expression, detected upon seeing the `]' generates the error. The default rule is to point at the first invalid character, which it does.

In a sense, the message should say 'invalid star expression', as in the second example. But then the pointer would need to point to the nothing between * and ]. If ^ pointed at * in the first example, I think the proposal for the second example should have a 6th ^ under * also.

To me, there is not really a bug, but a possible enhancement.

[lysnikolaou]

I agree that we can improve the A[*(1:2)] case. @sobolevn If you want to work on it, I'd be happy to review a PR. Otherwise, I can do it as well.