FuncAnimation being called too many times

Question

This is a continuation of a previous question I asked . I noticed the values being used to update my pie chart were incorrect. I have a list z that is being updated with the num iterator in my FuncAnimation function named update . Here is the code I'm working with:

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

numbers = [[6.166, 5.976, 3.504, 7.104, 5.14],
 [7.472, 5.888, 3.264, 6.4825, 7.168],
 [7.5716, 9.936, 3.6, 8.536, 2.808],
 [2.604, 2.296, 0.0, 6.144, 4.836],
 [7.192, 4.932, 0.0, 6.016, 8.808],
 [7.192, 5.5755, 3.694, 9.376, 9.108],
 [7.63616, 5.912, 3.968, 6.672, 3.192],
 [3.41049, 5.44, 4.004, 7.212, 3.6954],
 [4.3143, 6.364, 3.584, 7.44, 5.78],
 [4.992, 3.9692, 4.272, 0.0, 2.528]]
numbers = np.array(numbers)

colors = ["yellow", "red", "purple", "blue", "green"]
explode = [0.01, 0.01, 0.01, 0.01, 0.01]
labels = ["DM", "Bard", "Warlock", "Paladin", "Ranger"]
z = np.array([0,0,0,0,0]).astype(np.float)

fig,ax = plt.subplots()
y = []
def update(num):
    global y
    global z
    ax.clear()
    ax.axis('equal')     
    z += numbers[num]
    y.append(z)
    
    #output of different vairables#
    print(num, z, sum(z), len(y))

    pie = ax.pie(z, explode=explode, labels=labels, colors=colors, 
                 autopct='%1.1f%%', shadow=True, startangle=140)
    ax.set_title(sum(z))    
    
ani = animation.FuncAnimation(fig, update, frames=range(10), repeat=False)
ani.save('test.gif', writer='pillow', fps=1)

The output of the print() function looks like this:

0 [6.166 5.976 3.504 7.104 5.14 ] 27.89 1
0 [12.332 11.952  7.008 14.208 10.28 ] 55.78 2
1 [19.804  17.84   10.272  20.6905 17.448 ] 86.05450000000002 3
2 [27.3756 27.776  13.872  29.2265 20.256 ] 118.5061 4
3 [29.9796 30.072  13.872  35.3705 25.092 ] 134.3861 5
4 [37.1716 35.004  13.872  41.3865 33.9   ] 161.3341 6
5 [44.3636 40.5795 17.566  50.7625 43.008 ] 196.27959999999996 7
6 [51.99976 46.4915  21.534   57.4345  46.2    ] 223.65975999999995 8
7 [55.41025 51.9315  25.538   64.6465  49.8954 ] 247.42165 9
8 [59.72455 58.2955  29.122   72.0865  55.6754 ] 274.90395 10
9 [64.71655 62.2647  33.394   72.0865  58.2034 ] 290.66515 11
0 [70.88255 68.2407  36.898   79.1905  63.3434 ] 318.55514999999997 12

The print output shows the that numbers[0] is being added to itself before the num iterator increases by 1. After that, it works as intended where numbers[1] through numbers[9] are added together. But again, numbers[0] is added to numbers[9] for some reason.

The resulting gif's first frame displays this data: [12.332 11.952 7.008 14.208 10.28 ] 55.78 and the last frame displays this data: [64.71655 62.2647 33.394 72.0865 58.2034 ] 290.66515 which is okay since this is where the loop should stop.

I'd like to know what I'm doing wrong in this case; how can I correct the unexpected behavior of num ?

Answer 1

Without an init_func= passed to FuncAnimation , it will use the animation function itself as the initial state, which causes your doublet 0 . The documentation states :

init_func : callable, optional

A function used to draw a clear frame. If not given, the results of drawing from the first item in the frames sequence will be used. This function will be called once before the first frame.

You can simply pass an empty function to fix the problem.

def init():
    pass

(...)

ani = animation.FuncAnimation(fig, update, frames=range(10), init_func=init, repeat=False)