Cannot pass linewidths to plot_kde

[davipatti]

Describe the bug

Passing linewidths to contour_kwargs does not affect contour linewidths.

To Reproduce

import arviz as az

idata = az.load_arviz_data('non_centered_eight')
az.plot_kde(idata.posterior["mu"], idata.posterior["tau"], contour_kwargs=dict(linewidths=0))

A UserWarning is raised:

.../python3.13/site-packages/arviz/plots/backends/matplotlib/kdeplot.py:166: UserWarning: The following kwargs were not used by contour: 'linewidth'
  ax.contour(x_x, y_y, density, **contour_kwargs)

Updating plt.rcParams["lines.linewidth"] does affect linewidths.

From the UserWarning it looks like linewidths may be being updated to linewidth, but contour expects linewidths

Expected behavior

Linewidths to be passed to matplotlib contour.

Additional context

arviz 0.22.0

[davipatti]

This is coming from matplotlib.contour.ContourSet alias mapping:

>>> getattr(mpl.contour.ContourSet, "_alias_map")
{

...

  "linewidth": [
    "linewidths",
    "lw"
  ],

...

}

which gets used by matplotlib_kwarg_dealiaser:

arviz/arviz/plots/backends/matplotlib/__init__.py

Line 80 in 01c8b94

return normalize_kwargs(args, getattr(matplotlib_kwarg_dealiaser_dict[kind], "_alias_map", {}))

[davipatti]

I implemented a workaround here: main...davipatti:arviz:fixing-kde-linewidths

Happy to make that into a PR, but not sure if there's a better fix

[jordandeklerk]

Hi @davipatti, thanks for bringing this up! We will likely address this in https://github.com/arviz-devs/arviz-plots rather than here. We don't yet have 2D KDE plots via plot_kde() in there yet, but this will be fixed when it gets added.

Also, you may find https://python.arviz.org/en/latest/user_guide/migration_guide.html useful for the future.