[Python] I cannot animate the scatter plot in matplotlib. Every frame is the repeat of the...

I am writing a python script to animate data from a list of .xyz files using matplotlib. However, the animation is actually static because each frame of the animation is displaying the data from the first frame itself.

The format of the .xyz files is as follows:

0.0199995 0.02 0.0199999
0.0397943 0.02 0.0199997
0.059875 0.02 0.0199997
0.0799158 0.0199993 0.02
0.0999472 0.02 0.0199997
0.119963 0.0199992 0.02
0.139975 0.02 0.0199996
0.159982 0.02 0.0199996
0.179987 0.02 0.0199996
0.19999 0.0199992 0.02
0.219993 0.0199992 0.02
0.239994 0.0199992 0.02


First column represents X, second Y and third Z.

for i in range(num_of_frames):
# Reading the data from ./sph_sim_output/frame_%d.xyz, where %d is the frame number
data_x, data_y, data_z = get_pt_data("./sph_sim_output/frame_000000.xyz", i)
data.append((data_x, data_y, data_z)) #data_x, data_y, data_z are numpy vectors

fig = plt.figure()
ax = fig.add_subplot(projection="3d")
x, y, z = get_pt_data("./sph_sim_output/frame_000000.xyz", 0)
scatters = ax.plot(x,z,y) # I also tried this with ax.scatter

def update_pts(frame, data,scatters):
x = data[frame][0]
y = data[frame][1]
z = data[frame][2]
scatters._offset3d = (x, z, y)
return scatters

anim = animation.FuncAnimation(fig, update_pts, num_of_frames, fargs=(data,scatters), interval=60, blit=False)
output_filename = "waterdrop.mp4"
anim.save(output_filename, fps=60, bitrate=5000, writer=video_writer, extra_args=video_extra_args)
plt.close(fig)



The data is organized as follows: the data is a list of tuples and each tuple contains three numpy arrays. Please refer to line 4 of the code above. I am not really sure what I am missing. I looked through 1 or 2 examples online, but it still doesn't help. I have plotted individual frames and they seem to be fine. I am pretty sure the problem might be in update_pts function, I just cannot figure it out.

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