Store mouse click event coordinates with matplotlib

mpl_connect needs to be called just once to connect the event to event handler. It will start listening to click event until you disconnect. And you can use

fig.canvas.mpl_disconnect(cid)

to disconnect the event hook.

What you want to do is something like:

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(-10,10)
y = x**2

fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x,y)

coords = []

def onclick(event):
    global ix, iy
    ix, iy = event.xdata, event.ydata
    print (f'x = {ix}, y = {iy}')

    global coords
    coords.append((ix, iy))
    
    if len(coords) == 2:
        fig.canvas.mpl_disconnect(cid)

    return coords
cid = fig.canvas.mpl_connect('button_press_event', onclick)