matplotlib artist animation : title or text not changing

Question

I tried using matplotlib's ArtistAnimation. The text and titles of the figure are supposed to change in each frame, but they don't. I have read tons of posts on similar problems, but I still don't understand what is the solution. The demos don't show updating titles as far as I could find.

If anybody out there knows, I would be grateful!

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

fig =plt.figure()    
ims=[]

for iternum in range(4):
    plt.title(iternum)
    plt.text(iternum,iternum,iternum)
    ims.append([plt.scatter(np.random.randint(0,10,5), np.random.randint(0,20,5),marker='+'    )])
    #plt.cla()


ani = animation.ArtistAnimation(fig, ims, interval=500, blit=False,
                              repeat_delay=2000)
plt.show()

Answer 1

You need to supply the artists to animate as a list of sequences to the ArtistAnimation. In the code from the question you only supply the scatter, but not the text and title.
Unfortunately the title is also part of the axes and thus will not change even if supplied. So you may use a normal text instead.

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

fig, ax = plt.subplots()
ims=[]

for iternum in range(4):
    title = plt.text(0.5,1.01,iternum, ha="center",va="bottom",color=np.random.rand(3),
                     transform=ax.transAxes, fontsize="large")
    text = ax.text(iternum,iternum,iternum)
    scatter = ax.scatter(np.random.randint(0,10,5), np.random.randint(0,20,5),marker='+')
    ims.append([text,scatter,title,])


ani = animation.ArtistAnimation(fig, ims, interval=500, blit=False,
                              repeat_delay=2000)
plt.show()

You may consider using FuncAnimation instead of ArtistAnimation. This would allow to change the title easily.

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

fig, ax = plt.subplots()
ims=[]

text = ax.text(0,0,0)
scatter = ax.scatter(np.random.randint(0,10,5), np.random.randint(0,20,5),marker='+')


def update(iternum):
    plt.title(iternum)
    text.set_position((iternum, iternum))
    text.set_text(str(iternum))
    scatter.set_offsets(np.random.randint(0,10,(5,2)))

ani = animation.FuncAnimation(fig, update, frames=4, interval=500, blit=False,
                              repeat_delay=2000)
plt.show()

Answer 2

To animate artists, you have to return a reference to each artists in your ims[] array, including the Text objects.

However it doesn't work for the title, I don't know why. Maybe somebody with a better understanding of the mechanisms involved will be able to enlighten us.

Nevertheless, the title is just a Text object, so we can produce the desired effect using:

fig = plt.figure()
ax = fig.add_subplot(111)
ims=[]

for iternum in range(4):
    ttl = plt.text(0.5, 1.01, iternum, horizontalalignment='center', verticalalignment='bottom', transform=ax.transAxes)
    txt = plt.text(iternum,iternum,iternum)
    ims.append([plt.scatter(np.random.randint(0,10,5), np.random.randint(0,20,5),marker='+'    ), ttl, txt])
    #plt.cla()


ani = animation.ArtistAnimation(fig, ims, interval=500, blit=False,
                              repeat_delay=2000)