Turing Pattern Formation

Question

this is a snipped code from page 261 of the textbook "Introduction to the modeling and analysis of complex system". I don't know why my visualized output wouldn't flow with time.

import matplotlib
matplotlib.use("Qt5Agg")
from pylab import *
import numpy as np
import tkinter as tk

n = 100
Dh = 1. / n
Dt = 0.02

a, b, c, d, h, k = 1., -1., 2., -1.5, 1., 1. #parameters

Du = 0.0001 #diffusion constant of u
Dv = 0.0006

def initialize():
    global u, v, nextu, nextv
    u = zeros([n, n])
    v = zeros([n, n])
    for x in range(n):
        for y in range(n):
            u[x, y] = 1. + uniform(-0.03, 0.03) #small noise is added
            v[x, y] = 1. + uniform(-0.03, 0.03)
    nextu = zeros([n, n])
    nextv = zeros([n, n])

def observe():
    global u, v, nextu, nextv
    subplot(1, 2, 1)
    cla()
    imshow(u, vmin = 0, vmax = 2, cmap = cm.binary)
    title("u")
    subplot(1, 2, 2)
    cla()
    imshow(v, vmin = 0, vmax = 2, cmap = cm.binary)
    title("v")

def update():
    global u, v, nextu, nextv
    for x in range(n):
        for y in range(n):
            uC, uR, uL, uU, uD = u[x, y], u[(x+1)%n, y], u[(x-1)%n, y], \
                                u[x, (y+1)%n], u[x, (y-1)%n]
            vC, vR, vL, vU, vD = v[x, y], v[(x+1)%n, y], v[(x-1)%n, y], \
                                v[x, (y+1)%n], v[x, (y-1)%n]
            uLap = (uC + uR + uL + uU + uD - 4 * uC) / (Dh**2)
            vLap = (vC + vR + vL + vU + vD - 4 * vC) / (Dh**2)
            nextu[x, y] = uC + (a*(uC-h) + b*(vC-k) + Du*uLap) * Dt
            nextv[x, y] = vC + (c*(uC-h) + d*(vC-k) + Dv*vLap) * Dt
        
    u, nextu = nextu, u 
    v, nextv = nextv, v

import pycxsimulator
pycxsimulator.GUI(stepSize=50).start(func=[initialize,`your text` observe, update])

I've check the code. it is exactly the same as the one written in the book. I've also tried to update the libraries, but the problem remains.`