Pylint: E1133:not-an-iterable on query result

[davetapley]

Edit:

Caused by upstream bug:

• false not-an-iterable for class method with @overload (2.5.7 regression) pylint-dev/astroid#1015

Workaround is to use results.

---

Can anyone replicate this?

inputs = self.query(Input)
ids = [input.id for input in inputs] # Pylint: E1133:not-an-iterable 

Makes no sense because:

textual/src/textual/css/query.py

Lines 141 to 142 in 81531e8

	def __iter__(self) -> Iterator[QueryType]:
	return iter(self.nodes)

And following though Pylint code it seems that's all it should need:

1. https://github.com/pylint-dev/pylint/blob/a841a7d9eab654e423a115b4feaa857d5f807c88/pylint/checkers/typecheck.py#L2291-L2294
2. https://github.com/pylint-dev/pylint/blob/a841a7d9eab654e423a115b4feaa857d5f807c88/pylint/checkers/typecheck.py#L2250-L2257
3. https://github.com/pylint-dev/pylint/blob/a841a7d9eab654e423a115b4feaa857d5f807c88/pylint/checkers/utils.py#L1298-L1302
4. https://github.com/pylint-dev/pylint/blob/a841a7d9eab654e423a115b4feaa857d5f807c88/pylint/checkers/utils.py#L1223

Any ideas? 🤔

[davetapley]

Debugging I figured out it gets down to here and gets Const.NoneType for inputs. I don't know why, but I assume it then yields error because None isn't iterable.

... except none of Query return None 🤯

textual/src/textual/dom.py

Lines 1073 to 1083 in 81531e8

	@overload
	def query(self, selector: str | None) -> DOMQuery[Widget]:
	...
	@overload
	def query(self, selector: type[QueryType]) -> DOMQuery[QueryType]:
	...
	def query(
	self, selector: str | type[QueryType] | None = None
	) -> DOMQuery[Widget] | DOMQuery[QueryType]:

[davep]

Can anyone replicate this?

Always. It's been one of those things where I see it while I'm in the middle of something else, go "I really should make a note of that but I'm busy right now", and then forget once I'm done with the code I'm writing. It's been bugging me for ages now and I keep meaning to check what's what.

The short (but unsatisfying) answer is "use results"; would be good to get to the bottom of that though.

[davetapley]

@davep well I'm glad it's not just me 😁
Thanks for workaround.

I did some digging prior to seeing your reply, my notes if someone else wants to pick it up:

I use VSCode debug with launch.json (replace file.py with a file with a query in it):

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "pylint",
            "type": "python",
            "request": "launch",
            "module": "pylint",
            "justMyCode": false,
            "args": ["file.py"]
        },

Then break point here: https://github.com/pylint-dev/pylint/blob/a841a7d9eab654e423a115b4feaa857d5f807c88/pylint/checkers/typecheck.py#L2291-L2294

Add disabled break point here:
https://github.com/pylint-dev/astroid/blob/2d309cbb823e27d73bf695447a50f7875a852612/astroid/decorators.py#L94

Hit first break, then enable second break and continue.

Will hit raise InferenceError(**error.args[0]) with something like:

error.args[0]
{'node': <Comprehension l.73 ...7bc9233d0>, 'unknown': <AssignName.i l.73 a...7bc923450>, 'assign_path': None, 'context': <astroid.context.Inf...7ade519c0>}

which causes yield Uninferable, then inferred = Const.NoneType,
and here gives not is_iterable(inferred,.. 😞

But that's so deep in to astroid internals I have no idea why InferenceError is raised 🤔

[davetapley]

Posted to https://discuss.python.org/t/reproducible-but-incorrect-pylint-e1133-not-an-iterable-in-library/38633, and:
code-quality@python.org

So 🤞🏻

[davetapley]

@davep we have an answer, per:

• Reproducible but incorrect Pylint: E1133:not-an-iterable in library pylint-dev/pylint#9253 (comment)

Underlying issue is:

• false not-an-iterable for class method with @overload (2.5.7 regression) pylint-dev/astroid#1015

But currently unfixed and no workaround 😞