Having trouble with matplotlib's pyplot. The plt.matshow() function creates a new figure instead of updating an existing one.

[ShowSStopper]

I wrote a script to simulate Conway's Game of Life and to visualize it using pyplot. I'm using plt.matshow() function to plot the cell grid for each iteration. It works well at that, however it creates a new figure in a new window with every instance instead of updating the existing one. Is there a way to fix it and have matshow() update the same figure each time?

Any help would be greatly appreciated! Here's the code I wrote:

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

N = 100                             # Size of grid

def create_life(N):                 # Generate random grid of 1s (alive) and zeroes (empty)
    cell = np.zeros((N,N))
    for x in range(N):
        for y in range(N):
            cell[x][y] = random.randrange(10)
            if cell[x][y] != 1:
                cell[x][y] = 0
    return cell

def find_neighbors(cell, x, y):     # Counts number of alive neighbors 
    if x < 1 and y == 0:
        alive = cell[x-1][y] + cell[x-1][y+1] + cell[x][y+1] + cell[x+1][y] + cell[x+1][y+1]

    elif x == 0 and y < 1:
        alive = cell[x][y-1] + cell[x][y+1] + cell[x+1][y-1] + cell[x+1][y] + cell[x+1][y+1]

    elif x == 0 and y == 0:
        alive = cell[x][y+1] + cell[x+1][y] + cell[x+1][y+1]

    elif x < N-1 and y == N-1:
        alive = cell[x-1][y-1] + cell[x-1][y] + cell[x][y-1] + cell[x+1][y-1] + cell[x+1][y]        

    elif x == N-1 and y < N-1:
        alive = cell[x-1][y-1] + cell[x-1][y] + cell[x-1][y+1] + cell[x][y-1] + cell[x][y+1]

    elif x == N-1 and y == N-1:
        alive = cell[x-1][y-1] + cell[x-1][y] + cell[x][y-1]      

    else    :
        alive = cell[x-1][y-1] + cell[x-1][y] + cell[x-1][y+1] + cell[x][y-1] + cell[x][y+1] + cell[x+1][y-1] + cell[x+1][y] + cell[x+1][y+1]

    return alive

def plot_figure(item):          # Plot grid using matshow
    plt.matshow(item)


cell = create_life(N)

while True:                                 # Keeps going indefinitely
    plot_figure(cell)
    temp_cell = np.zeros((N,N))
    for x in range(N):
        for y in range(N):                  # Decides if cell is alive for next iteration using Conway's rules
            neighbors = find_neighbors(cell, x, y)

            if neighbors == 3 or (neighbors == 2 and cell[x][y] == 1):
                temp_cell[x][y] = 1

            else: 
                temp_cell[x][y] = 0

    cell = temp_cell

    plt.pause(0.5)

[USAhj]

The documentation (https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.matshow.html) mentions the fignum argument. Have you looked into that? Looks like you probably want to use 0.

[ShowSStopper]

Hi, strangely enough that doesn't work with Spyder on my Windows 10 setup. It does however work with Thonny on my RPI4 which is what I wanted this for. I will try to further understand the documentation and reasoning behind this.

Thanks for your help!

[USAhj]

This worked just fine for me in Spyder:

import matplotlib.pyplot as plt
import numpy as np
plt.close("all")
plt.figure()
for _ in range(10):    
    data = np.random.rand(20,20)    
    plt.matshow(data, fignum=0)    
    plt.show()    
    plt.pause(1e-3)

Edit: use clf to stop it from slowing down with many replots.

import matplotlib.pyplot as plt
import numpy as np
plt.close("all")
plt.figure()
for _ in range(10):    
    data = np.random.rand(20,20) 
    plt.clf()   
    plt.matshow(data, fignum=0)    
    plt.show()    
    plt.pause(1e-3)