Extract points from contour plot in python

Question

I am interested in extracting the data of the couples (x,y) used to mark the yellow level line (corresponding to z=0) in this contour plot:

Here is a sample of the code used to generate the plot, from data (X,Y,Z):

import matplotlib.pyplot as plt
from scipy.interpolate import griddata

z_i = griddata((X, Y), Z, (x_i[None,:], y_i[:,None]), method='cubic')
CS = plt.contourf(x_i, y_i, z_i, 50, cmap=plt.cm.Blues)
plt.colorbar() 
plt.contour(x_i, y_i, z_i, 0, colors='yellow')