Implement freq_at_index method for GenericSpectrogram (fixes #129)

[Monier-Ayman]

PR Description

This pull request adds a new method freq_at_index(idx) to the Spectrum class (GenericSpectrogram).
The method returns the frequency corresponding to a given index on the frequency axis (freq_axis).

Motivation

Converting between indices and frequencies is useful for machine learning, data analysis, and other post-processing operations on spectrogram data.

Changes

• Added freq_at_index(idx) in radiospectra/spectrum.py
• Added tests for valid and out-of-bounds indices in radiospectra/tests/test_spectrum.py

Issue

Fixes #129

[Amityush-lgtm]

Hey @Monier-Ayman! Thanks for working on this. I’m new to radiospectra but I’m trying to learn by following along.
I noticed CI is still red on py313 (and pre-commit). I’m going to pull your branch and try to reproduce locally.
If you want, I can paste the exact failing traceback from py313 here once I have it, or suggest a small patch.

[Amityush-lgtm]

Hi @Monier-Ayman,

I pulled the branch and reproduced the CI failures locally. Two quick things:

In radiospectra/tests/test_spectrum.py, pytest is complaining that ValueError is too broad. You can fix it by adding the match argument:
Following this link: https://docs.astral.sh/ruff/rules/pytest-raises-too-broad/

Instead of :
with pytest.raises(ValueError): ...
Change it to:
with pytest.raises(ValueError, match="out of bounds"): ...

(use whatever string matches the actual error message)

pre-commit: looks like import sorting/formatting. Running this fixed it for me:

pre-commit run --all-files

One question on scope: this adds freq_at_index on Spectrum but issue #129 mentions GenericSpectrogram. Do you want the helper on GenericSpectrogram too, or is Spectrum the intended place now?

[Amityush-lgtm]

@Monier-Ayman Your latest fix is almost there! I think the reason it's still failing the test is that match="Index out of bounds" is looking for those words side-by-side. Since the error message is Index 5 out of bounds, the 5 breaks the match. If you change it to just match="out of bounds", it will pass.

[Monier-Ayman]

Hi @Cadair and @samaloney, when you have a chance, could you please review this PR? It adds the freq_at_index(idx) method to GenericSpectrogram and includes tests for valid and out-of-bounds indices. Thanks!

[samaloney]

@Monier-Ayman thanks for the PR but as I mentioned over on the issue #129 I'm not sure this is the best place to start as this will be core aspect of the upcoming GSOC project.