Reproducible but incorrect Pylint: E1133:not-an-iterable in library

[davetapley]

Bug description

# iter_bug.py

from textual.app import App
from textual.widgets import Input


class MyApp(App[None]):
    def whatever(self):
        print([i.id for i in self.query(Input)])

Configuration

No response

Command used

pylint iter_bug.py

Pylint output

************* Module iter_bug
iter_bug.py:7:29: E1133: Non-iterable value self.query(Input) is used in an iterating context (not-an-iterable)

Expected behavior

No errors.

Pylint version

pylint 3.0.2
astroid 3.0.1
Python 3.11.6 (main, Nov  2 2023, 02:14:33) [GCC 9.4.0]

OS / Environment

Ubuntu 20.04.6 LTS

Additional dependencies

textual == 0.40.0

[davetapley]

Creating as requested here. Initially reported here:

• Pylint: E1133:not-an-iterable on query result Textualize/textual#3671

---

Some notes:

All overloads of a method query return an instance of DOMQuery:
https://github.com/Textualize/textual/blob/81531e87647eae26b83ad31f1941016b4f2bab41/src/textual/dom.py#L1073-L1083

and DOMQuery implements __iter__:

https://github.com/Textualize/textual/blob/81531e87647eae26b83ad31f1941016b4f2bab41/src/textual/css/query.py#L141-L142

By my reckoning that should be enough? 🤔

---

texual maintainer suggests workaround of using a results method they added, which works:
https://github.com/Textualize/textual/blob/896aa9f9244ce852659946bb3abc8551b38bbb03/src/textual/css/query.py#L309-L310

---

I did some 👀 myself:

I use VSCode debug with launch.json:

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

Then break point here:

pylint/pylint/checkers/typecheck.py

Lines 2291 to 2294 in a841a7d

	@only_required_for_messages("not-an-iterable")
	def visit_listcomp(self, node: nodes.ListComp) -> None:
	for gen in node.generators:
	self._check_iterable(gen.iter, check_async=gen.is_async)

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 🤔

[jacobtylerwalls]

Thanks for the investigation. From the source for query, which you linked, I noticed the use of @overload. We lack support for that (see pylint-dev/astroid#1015), so that's my best guess for why Uninferable turns up.

More specifically, though, the not-an-iterable check should quiet itself when Uninferable turns up. That's a trivial patch. Coming right up!

[jacobtylerwalls]

More specifically, though, the not-an-iterable check should quiet itself when Uninferable turns up. That's a trivial patch. Coming right up!

Ah, it does that already. I didn't notice this part of your report:

then inferred = Const.NoneType,

So really this is just a duplicate of pylint-dev/astroid#1015, unfortunately. Sorry there is no workaround at the moment!