Why do I get an error when running this example code?

Question

I tried to run the example code from following site in Python 3.8:

https://www.demo2s.com/python/python-matplotlib-animation-animate-decay.html

However, I get the following error:

C:\Users\username\anaconda3\lib\site-packages\matplotlib\animation.py:889: UserWarning: Animation was deleted without rendering anything. This is most likely not intended. To prevent deletion, assign the Animation to a variable, e.g. anim, that exists until you have outputted the Animation using plt.show() or anim.save(). warnings.warn(

Note that this is the full error that I get.

How can I solve this?

Here is the complete code:

import itertools

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation


def data_gen():# www  .de  m  o2  s.c o  m
    for cnt in itertools.count():
        t = cnt / 10
        yield t, np.sin(2*np.pi*t) * np.exp(-t/10.)


def init():
    ax.set_ylim(-1.1, 1.1)
    ax.set_xlim(0, 10)
    del xdata[:]
    del ydata[:]
    line.set_data(xdata, ydata)
    return line,

fig, ax = plt.subplots()
line, = ax.plot([], [], lw=2)
ax.grid()
xdata, ydata = [], []


def run(data):
    # update the data
    t, y = data
    xdata.append(t)
    ydata.append(y)
    xmin, xmax = ax.get_xlim()

    if t >= xmax:
        ax.set_xlim(xmin, 2*xmax)
        ax.figure.canvas.draw()
    line.set_data(xdata, ydata)

    return line,

ani = animation.FuncAnimation(fig, run, data_gen, interval=10, init_func=init)
plt.show()