GeezerVison

Since the error messages will not change I removed the NEWS blurb and added the skip news label. Also updated the initial PR description.

I have updated the PR with the latest changes from #20003

Simpler example that gets the same error:

>>> for f, g() in 10: pass

And this too:

>>> for f(), g in 10: pass

I recommend extreme caution here. If I can poke holes this quickly, I worry that we may be causing a regression if we rush this in before beta1. We obviously don't have the right testing strategy here.

There's nothing that says we have to get this level of detail right in beta1.

Simpler example that gets the same error:

>>> for f, g() in 10: pass

And this too:

>>> for f(), g in 10: pass

I recommend extreme caution here. If I can poke holes this quickly, I worry that we may be causing a regression if we rush this in before beta1. We obviously don't have the right testing strategy here.

There's nothing that says we have to get this level of detail right in beta1.

I pushed a version that I think is pretty close, but I'm not 100% certain. I agree, that there's no rush to land this and that we should test a bit more.

Could you explain this a bit more? I don't get it.

What I meant is that; since this PR already generates 'can't use starred expression here' error messages for some cases, it isn't fully compatible with the old parser. del *a, b was the example I tested both on the old parser and pegen (with this PR applied), and they give different results.

For starred expressions, the message differs from the old parser;

(new parser)
>>> del *a, b
SyntaxError: cannot delete starred

(old parser)
>>> del *a, b
SyntaxError: can't use starred expression here

Could you explain this a bit more? I don't get it.

What I meant is that; since this PR already generates 'can't use starred expression here' error messages for some cases, it isn't fully compatible with the old parser. del *a, b was the example I tested both on the old parser and pegen (with this PR applied), and they give different results.

For starred expressions, the message differs from the old parser;

(new parser)
>>> del *a, b
SyntaxError: cannot delete starred

(old parser)
>>> del *a, b
SyntaxError: can't use starred expression here

I think I understand now.

Indeed the old parser used to produce can't use starred expression here and the error message has changed since then. But this PR does not change it, it actually just adopts the changed error message which was introduced in #19911.

Also, I can remember @pablogsal mentioning somewhere that changing just the message is okay in terms of backwards-compatibility.

Indeed the old parser used to produce can't use starred expression here and the error message has changed since then. But this PR does not change it, it actually just adopts the changed error message which was introduced in #19911.

I see, didn't notice that. Sorry for distraction.

Also, I can remember @pablogsal mentioning somewhere that changing just the message is okay in terms of backwards-compatibility.

So, is this error will be kept (cannot delete starred) or would it be cool to have a patch that customizes errors for starred context (can't use starred expression here)?

I like the cannot delete starred one better. When I see it, I immediately know without even looking at the line of the error that it's got to do with a del statement. On the contrary, can't use starred expression here does not give enough context, I feel. But really, I don't feel very strongly either way. What do the others think?

Same here.

FYI there is an unrelated CI failure on macOS in test_asyncio.

Thanks @lysnikolaou for the PR, and @pablogsal for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

Sorry, @lysnikolaou and @pablogsal, I could not cleanly backport this to 3.9 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 01ece63d42b830df106948db0aefa6c1ba24416a 3.9

@lysnikolaou Could you do the manual backport?

@lysnikolaou Could you do the manual backport?

Of course, on it.

GH-20973 is a backport of this pull request to the 3.9 branch.

FYI, appears to have caused a regression: https://bugs.python.org/issue41060.
This causes with a as b to crash the interpreter