list_group undefined if python is run with -O flag

[uiop860]

So we have been trying to figure out this bug for a while, and i realized we are running python with the -O flag which means these lines don't get executed and therefore list_group is undefined.

docling-core/docling_core/transforms/serializer/markdown.py

Lines 173 to 175 in e234480

	assert item.parent and isinstance(
	(list_group := item.parent.resolve(doc)), ListGroup
	)

My linter actually caught this but, i didn't realize for a while.

https://docs.astral.sh/ruff/rules/assignment-in-assert/

[dosubot]

Hi @uiop860! I'm Dosu and I’m helping the docling-core team.

This bug happens because the assignment to list_group uses the walrus operator inside an assert statement. When Python runs with the -O flag, all assert statements are skipped—including any assignments inside them—so list_group is never defined, which leads to a NameError when it's used immediately after. This is exactly the kind of issue flagged by Ruff rule RUF018, which warns against assignments in asserts because they disappear under -O and can leave variables undefined, causing subtle and hard-to-debug runtime errors.

Best practice: always assign variables outside of assert statements, and use asserts only for checks, not for side effects or assignments. In this case, assign list_group before the assert, then assert its type or properties as needed. This pattern was only found in the referenced location in markdown.py and does not appear to be widespread elsewhere in the codebase, but it's a critical fix for -O compatibility and code reliability.
See the relevant code context here.

To reply, just mention @dosu.

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