producto de matrices

a=[[1,3,5],[2,4,8],[8,4,7]]
b=[[4,9,3],[7,4,3],[5,2,1]]
matriz=[[0,0,0],[0,0,0],[0,0,0]]
numeros=[]
count=0
j=0
m=0
while j<len(a)*len(b):
    sum=0
    for i in range (0, len(a)):
        sum+=a[m][i]*b[i][count]
    if j==2 :
       m+=1
    if j==5:
       m+=1
    count+=1
    if count>=3 :
       count=0
    numeros.append(sum)
    j+=1
cont=0
for j in range(0,len(a)):
    for m in range(0,len(b)):
        matriz[j][m]=numeros[cont]
        cont+=1
print("multiplicarlas matrices \n A",a,"\n","y B",b,"\n","es igual a",matriz)