Plotting an ellipse but ellipse is not showing up

Question

I am attempting to plot an ellipse surrounding scattered data points, but when the pyplot displays my plot only the data points are showing up and ellipse isn't. Do I need to install the patch somehow?

Here is my code:

from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as pp
import numpy as np
from matplotlib import cm
import pandas as pd
from matplotlib.patches import Ellipse

data_to_plot = pd.read_csv("positions.csv", sep = ",", index_col=False)
xs = data_to_plot['x']
ys = data_to_plot['y']
zs = data_to_plot['z']

covxy = np.cov(xs, ys)
lambda_xy, vxy = np.linalg.eig(covxy)
lambda_xy = np.sqrt(lambda_xy)

ax1 = pp.subplot(221)
for j in xrange(1, 4):
    ell = Ellipse(xy=(xav, yav),
                  width=lambda_xy[0]*j*2, height=lambda_xy[1]*j*2,
                  angle=-np.rad2deg(np.arccos(vxy[0, 0])))
    ell.set_facecolor('none')
    ax1.add_artist(ell)
ax1.set_xlabel("x distance from the sun / AU")
ax1.set_ylabel("y distance from the sun / AU")
pp.scatter(xs, ys)

pp.xlim(xav-0.001,xav+0.0013)
pp.ylim(yav-0.001,yav+0.001)

Answer 1

ell.set_facecolor('none') seems counterproductive. If the intention is to show the ellipse, it should not have 'none' as color. Or it should have at least an edgecolor being set, eg

ell.set_edgecolor("limegreen")

Or consider giving the colors as arguments to the ellipse

Ellipse(..., fc="none", ec="limegreen")