Make "perhaps you missed a comma?" hint in syntax warnings less cryptic

[ncoghlan]

Feature or enhancement

Proposal:

Syntax warnings for code like [][""], [](), and 1[2] finish with the hint "perhaps you missed a comma?"

>>> lambda: 1[2]
<python-input-23>:1: SyntaxWarning: 'int' object is not subscriptable; perhaps you missed a comma?
<function <lambda> at 0x705dfb04b920>

When this came up in a review of currently emitted syntax warnings, it took me a moment to realise that it was suggesting the two subexpressions might have been supposed to be separate items in a sequence definition.

While I expect this would be clearer in the context of an actual warning, in isolation it felt very cryptic. Perhaps it would make sense to expand the hint to "did you miss a comma to separate sequence elements?"

Edit: Amended proposed text as @hugovk suggested

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-140764: Make "missed comma" syntax warning less cryptic #140893

[hugovk]

We can also be more direct and concise:

"Did you miss..."

Rather than:

"Perhaps you missed..."

[StanFromIreland]

Marking this as easy, contributors beware this is easy C, not easy Python.

[7576457]

I’d like to work on this

[StanFromIreland]

Go ahead!

[adqm]

"miss" is also an interesting choice of verb there because it has multiple meanings. Maybe "forget" or "omit" or something might be more apt?

Also, even though it might require a more-substantial rearrangement of the code than just changing the message, maybe it would be good only to emit this warning in contexts where commas make sense (list/set/dict displays, argument lists, etc)?

[serhiy-storchaka]

The original message was written taking existing syntax warning "assertion is always true, perhaps remove parentheses?" and syntax error "expression cannot contain assignment, perhaps you meant "=="?" as examples. @gvanrossum then corrected it.