Legend display for bubble sizes in geom_point

[vale46]

Hello - thanks again for your great work to implement ggplot2 functionality in Python!

My question is about an enhancement to the legend created when drawing a geom_point() plot with a size mapped to a continuous variable. Here's a minimal demo example:

import polars as pl
import plotnine as p9
import numpy as np

rng = np.random.default_rng(12345)
n=150

df = pl.DataFrame({
    "x": 10 * rng.random(size=n),
    "y": 5 * rng.random(size=n),
    "var1": 100 * rng.random(size=n),
})

(
    p9.ggplot(df, p9.aes("x", "y", size="var1"))
    + p9.geom_point(color='black', fill='white')
)

which creates the following plot with point sizes mapped to var1.

All good so far, but I'd like to show the legend entries as nested circles, rather than the conventional stacked style as shown on the plot. The nested style is not only aesthetically pleasing but makes the relative sizes easier to compare. I have seen this style of legend used in The Economist and The Wall Street Journal as well as other publications. (see example below)

Not sure if ggplot2 offers this out of the box, but think this would be a nice feature!

Thanks

[has2k1]

This a very custom legend that requires a new guide_* class and a new drawing function similar to geom_point.draw_legend but a little more sophisticated.

This may be a good candidate for an extension package.