False positive F401 due to %%ipytest line in notebook

[tovrstra]

Keywords to find existing issue: F401 and ipytest. The following is very similar, but still different, it seems: #10454

A minimal working example would be a Jupyter notebook with the following two cells:

import ipytest
import pytest

ipytest.autoconfig()

%%ipytest

def test_simple():
    with pytest.raises(TypeError):
        print(1 + "a")

Ruff will report F401 (unused-import) for the line import pytest.

To reproduce the issue, create a notebook with the above cells, called bug.ipynb and run the command:

ruff check demos/bug.ipynb --fix

I've tested with with ruff 0.6.3 and 0.6.9. I have the following in my pyproject.toml, but I don't think these settings matter:

[tool.ruff]
line-length = 100
target-version = "py311"

[tool.ruff.lint]
select = ["E", "F", "UP", "B", "I", "PGH", "PL", "RUF"]
ignore = ["E741", "PLR2004", "PLR0913", "PLR0912", "PLW2901", "PLR0915"]

As a workaround, one can (obviously) add a comment # noqa: F401 to the import line

When removing the line %%ipytest, the problem goes away, but it that doesn't help because the line is doing something useful.

Given the easy workaround, this is probably not urgent.

By the way, thanks for creating Ruff!

[MichaReiser]

I don't fully understnad yet what's happening but the code works as expected when I change %%ipytest to %ipytest

[MichaReiser]

@dhruvmanila do you have an idea why using the %%magic form makes the diagnostic appear?

[dhruvmanila]

Yeah, the double percent like %%magic are cell magics which apply to the entire cell and so we ignore those cells except for a few:

ruff/crates/ruff_notebook/src/cell.rs

Lines 217 to 244 in fd5fcc4

	// These cell magics are special in that the lines following them are valid
	// Python code and the variables defined in that scope are available to the
	// rest of the notebook.
	//
	// For example:
	//
	// Cell 1:
	// ```python
	// x = 1
	// ```
	//
	// Cell 2:
	// ```python
	// %%time
	// y = x
	// ```
	//
	// Cell 3:
	// ```python
	// print(y) # Here, `y` is available.
	// ```
	//
	// This is to avoid false positives when these variables are referenced
	// elsewhere in the notebook.
	!matches!(
	command,
	"capture" | "debug" | "prun" | "pypy" | "python" | "python3" | "time" | "timeit"
	)

While, the single percent like %magic are line magics that considers only the line on which it is defined.

[MichaReiser]

Oh that's good to know. Thanks. So the solution here would be to move the %%ipytest command to its own cell?

[dhruvmanila]

I think it is in its own cell. It's just that the entire cell is currently ignored by Ruff because ipytest is being special cased. I think we could do it because the lines following the ipytest magic should contain valid Python code. @tovrstra I'm not familiar with the magic command so just want to confirm if that's valid. I can check as well.

[MichaReiser]

What I mean is that a possible workaround is to change the notebook to have three cells:

import ipytest
import pytest

ipytest.autoconfig()

%%ipytest

def test_simple():
    with pytest.raises(TypeError):
        print(1 + "a")

[dhruvmanila]

I think then the magic command won't work because it won't be applied to the cell it was previously targeting.

[dhruvmanila]

I just tested it, it's safe to include ipytest in the allowed cell magic in the following code. And, the implementation of %%ipytest also confirms that it runs the cell first and then runs pytest on top of it. So, the cell can be considered as being without the magic itself.

ruff/crates/ruff_notebook/src/cell.rs

Lines 241 to 244 in fd5fcc4

	!matches!(
	command,
	"capture" | "debug" | "prun" | "pypy" | "python" | "python3" | "time" | "timeit"
	)

[tovrstra]

Thank you all for the comments and the fix. My apologies for commenting late. Indeed, the %%ipytest should be on the first line of the cell containing unit tests. It means "this cell contains unit tests". If it is put in a separate cell or further down, the tests will not get executed when running the cell.