Matplotlib animation displays extra plot

[ahwillia]

This is driving me a bit nuts. I'm using the following code to produce a simple animation. It works in the sense that the movie gets displayed but I also get an extra plot in my notebook, showing one of the frames of the movie.

Using IJulia.clear_output() only deletes the movie I want! The bonus frame stays around.

My guess is that this has something to do with PyCall (the equivalent example in a Jupyter notebook with a Python kernel works fine, so I'm convinced this is specific to Julia)

Code:

using PyCall
import IJulia
@pyimport matplotlib.animation as animation
using PyPlot

function showanim(filename)
    base64_video = base64encode(open(readbytes, filename))
    display("text/html", """<video controls src="data:video/x-m4v;base64,$base64_video">""")
end

A = randn(20,20,20)

fig = figure(figsize=(2,2))

function make_frame(i)
    imshow(A[:,:,i+1],interpolation="none")
end

anim = animation.FuncAnimation(fig, make_frame, frames=size(A,3), interval=20)
anim[:save]("test2.mp4", bitrate=-1, extra_args=["-vcodec", "libx264", "-pix_fmt", "yuv420p"]);
showanim("test2.mp4");

Screenshot:

[JobJob]

Hi, it's a bit kludgy, but I tried adding empty!(IJulia.displayqueue) just before the showanim and that works.

@stevengj should IJulia.clear_output possibly include empty!(displayqueue)? I have limited experience with clear_output so I'm not sure, but it helps for this particular case.

[ahwillia]

Thanks, you are a hero. As a workaround I'll put empty!(IJulia.displayqueue) at the top of the showanim function.

Should I close this, or leave open in hopes of a less "kludgy" solution?

[JobJob]

Good. I think we can leave it open and wait for @stevengj to weigh in.

[stevengj]

Emptying the displayqueue on clear_output seems very reasonable.

As an alternative, you could also do

withfig(fig) do
    anim = animation.FuncAnimation(fig, make_frame, frames=size(A,3), interval=20)
    anim[:save]("test2.mp4", bitrate=-1, extra_args=["-vcodec", "libx264", "-pix_fmt", "yuv420p"])
end

The withfig function was designed for using PyPlot with Interact.jl animations, and what it does is to eliminate side effects from plotting (e.g. imshow will no longer push a figure to display).