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FuncAnimation only triggered on assignment #18893
Description
Bug report
Bug summary
FuncAnimation gets only triggered/executed when it is assigned. For example _ = animation.FuncAnimation(*params) and anim = animation.FuncAnimation(*params) work, whereas animation.FuncAnimation(*params) does not work.
Code for reproduction
An example is the decay example from the matplotlib homepage.
I just changed ani = animation.FuncAnimation(fig, run, data_gen, interval=10, init_func=init) to animation.FuncAnimation(fig, run, data_gen, interval=10, init_func=init)
import itertools
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
def data_gen():
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,
animation.FuncAnimation(fig, run, data_gen, interval=10, init_func=init) # This is the only line different from the original example
plt.show()Actual outcome
The animation does not start.
Expected outcome
The animation starts.
This problem only occurs for matplotlib==3.3.x. With matplotlib==3.2.2 this issue does not occur.
Matplotlib version
- Operating system: macOS 10.15.7
- Matplotlib version: 3.3.x
- Matplotlib backend (
print(matplotlib.get_backend())):TkAgg - Python version: 3.8.6
- numpy version: 1.19.3
I installed phthon via homebrew and matplotlib in a venv via pip (pip3 install matplotlib)
Activity
jklymak commentedon Nov 4, 2020
I believe that is on purpose to avoid garbage collection of the animation.
timhoffm commentedon Nov 4, 2020
It's documented here: https://matplotlib.org/devdocs/api/animation_api.html:
However that might not be very discoverable. We could additionally mention it in the class docstring and/or the examples themselves.
HaaLeo commentedon Nov 4, 2020
@timhoffm thx for clarification 👍🏼 . I only searched the changelog of v3.3.0 and could not find anything.
Please feel free to close the issue then if you decide to not take further action.