[FIXED] How to plot a hollow circle with gradient/fadeout/glow in Matplotlib?

Issue

I would like to plot a circle of a given outer radius which would have an empty hole of a given inner radius. Then the resulting ring would have a fade-out gradient fill, however starting not from the center of the circle, but from the border of the inner circle. In Photoshop it's called "glow", from what I know. Is something like this possible?
here's an image showing what I mean

Solution

You could create an image from a function that is zero inside the circle and goes from 1 to 0 on the outside.

Using a colormap that goes from fully transparent white to opaque red would not only interpolate the color but also the transparency.

Here is an example, placing some text to demonstrate the effect of the transparency.

import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
import numpy as np

inner_radius = 1
outer_radius = 3
center_x = 6
center_y = 4
halo_color = 'gold'
# center_color = 'none' # for an empty center
center_color = '#ff334466'  ## redish with 25% alpha
xmin = center_x - outer_radius
xmax = center_x + outer_radius
ymin = center_y - outer_radius
ymax = center_y + outer_radius
x, y = np.meshgrid(np.linspace(xmin, xmax, 500), np.linspace(ymin, ymax, 500))
r = np.sqrt((x - center_x) ** 2 + (y - center_y) ** 2)
z = np.where(r < inner_radius, np.nan, np.clip(outer_radius - r, 0, np.inf))
cmap = LinearSegmentedColormap.from_list('', ['#FFFFFF00', halo_color])
cmap.set_bad(center_color)
plt.text(center_x, center_y, "Test", size=50, color='b')
plt.imshow(z, cmap=cmap, extent=[xmin, xmax, ymin, ymax], origin='lower', zorder=3)
plt.axis('equal')
plt.show()

Answered By - JohanC