Seem failure to generate random numbers

Question

I have inspect about generates of random number. You can see that random numbers is generated four times in the nested loop:

prob_burn = 0.1
for times in range(20):
        
    for i in range(1, row-1):
        for j in range(1, col-1):

            if yards[i][j] == 2:
                rand = np.random.rand() 
                if yards[i+1][j] == 1: # South
                    if rand < prob_burn:
                        yards[i+1][j] = 2
                    else:
                        yards[i+1][j] = 1

                rand = np.random.rand()        
                if yards[i][j+1] == 1: # East
                    if rand < prob_burn:
                        yards[i][j+1] = 2 
                    else:
                        yards[i][j+1] = 1 

                rand = np.random.rand()        
                if yards[i-1][j] == 1: # North
                    if rand < prob_burn:
                        yards[i-1][j] = 2
                    else:
                        yards[i-1][j] = 1

                rand = np.random.rand()
                if yards[i][j-1] == 1: # West
                    if rand < prob_burn:
                        yards[i][j-1] = 2 
                    else:
                        yards[i][j-1] = 1

                yards[i][j] = 0
            else:
                continue
    print(rand)

when the 'yards' multidimensional array code is:

row = 42
col = row

yards = [[0 for i in range(col)] for j in range(row)]
prob_tree = 0.8 

for i in range(1, row-1):
    for j in range(1, col-1):
        rand = np.random.rand()
        if rand < prob_tree:
            yards[i][j] = 1
        else:
            yards[i][j] = 0

yards[6][6] = 2

I have been confused when compiled this. Its gives the output:

0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566
0.9858723195931566

That's seem not really generating random of numbers between [0,1]. I have already tried to growed that 'times' loop more than 20, but still gives a similar characteristic. How to solve it?

Answer 1

print is called in the outmost loop, so it gets only the last value of rand.

just print the rand value after each rand call, and you will see it is really working, and different each time.

        rand = np.random.rand()
        print(rand)

You will get something like:

0.360516239461243
0.5027246719138412
0.5227674056389815
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266
0.34277438417911266