I'm trying to animate two subplots, each with multiple lines. I am using Matplotlib, and I am using the FuncAnimation
, which is used by many of the animation examples.
If I try to animate it, I only get the result of the first frame:
If I manually call my update_lines
function, it works fine.
Below is the full code (uncommenting the 3 indicated lines in main()
works, but I would like to see it update in real-time, hence trying to use the animation).
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
def make_subplots():
def setup_axes(axes):
for ax in axes:
ax.set_xbound(0, 100) # bound will change as needed.
ax.set_ylim(0, 1) # limit won't change automatically.
def make_lines(axes):
labels = ('a', 'b', 'c')
lines = []
for ax in axes:
ax_lines = []
for label in labels:
x, y = [0], [0]
line, = ax.plot(x, y, label=label) # comma for unpacking.
ax_lines.append((line, x, y))
lines.append(ax_lines)
return lines
fig, axes = plt.subplots(2, 1, sharex=True, sharey=True)
lines = make_lines(axes)
setup_axes(axes)
return fig, axes, lines
def make_data():
for i in xrange(100):
print 'make_data():', i
data = dict()
for label in ('a', 'b', 'c'):
from random import random
data[label] = random()
yield (i + 1, data)
def update_lines(data, lines):
print 'update_lines():', data, lines
updated_lines = []
for ax_lines in lines:
for line, x, y in ax_lines:
label = line.get_label()
x.append(data[0])
y.append(data[1][label])
line.set_data(x, y)
updated_lines.append(line)
def main():
fig, axes, lines = make_subplots()
# Uncomment these 3 lines, and it works!
# new_data = make_data()
# for data in new_data:
# update_lines(data, lines)
FuncAnimation(fig=fig,
func=update_lines,
frames=make_data,
fargs=(lines,),
interval=10,
blit=False)
plt.show()
if __name__ == '__main__':
main()
So, I was digging around the source-code of matplotlib.animation.Animation
, and I noticed these lines in the __init__()
function:
# Clear the initial frame
self._init_draw()
# Instead of starting the event source now, we connect to the figure's
# draw_event, so that we only start once the figure has been drawn.
self._first_draw_id = fig.canvas.mpl_connect('draw_event', self._start)
This looks right so far. The self._init_draw()
call draws my first frame immediately. Then the animation-object hooks into the figure-object and waits for the figure to be shown before attempting to draw any more frames for the animation.
The keyword is: animation-object. Since I wasn't planning on using the animation instance later (for example, to draw a movie), I didn't assign it to a variable. In fact, I was being yelled at by pyflakes because Local variable '...' is assigned to but never used
.
But because all of the functionality relies on the hook, when the canvas is finally shown I presume Python's garbage collection has removed the Animation instance---since it was never assigned to a variable---and therefore the animation can never be started.
Simply assign the instance FuncAnimation
instance to a variable, and everything works as expected!
anim = FuncAnimation(fig=fig,
func=update_lines,
frames=make_data,
fargs=(lines,),
interval=10,
blit=False)
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