python程序无法与条件语句一起正常工作

Question

  def matrixADD(A,B):
    minilist=[]
    Z = []
    a=-1
    b=-1

The condition in while loop below is not being followed for some reason so the index goes out of range. To fix it I had to add nested if statement below to break out of the loop. It is very weird I was wondering why is it not working without the if statement?

    while len(A)!=len(Z):
        x=-1
        y=-1
        a=a+1
        b=b+1   

        if len(minilist)!=0:
            Z.append(minilist)
            if len(A)==len(Z):
                break
        minilist=[]    

        while len(A[a])!=len(minilist):
            for numbers in A[a]:
                x=x+1
                y=y+1            
                answer=(A[a][x]+B[b][y])
                minilist.append(answer)

    return Z

def main():
    #Test matrices
    A = [[2,4], [7,0], [6,3]]
    B = [[3,1], [-1,8], [-3, 3]]
Z=matrixADD(A,B)
    print("A + B:",Z)

main()

Hi guys. I wrote this program and it works just fine but I was having some trouble with 1 thing (indicated above)

Thanks for your input guys :)

Answer 1

It looks like you expected the loop to end as soon as the element was added that caused the list sizes to match. That's not how loops work.

The while loop condition is only tested at the start of each iteration of the loop. If it stops being true in the middle of the loop, Python won't notice until the start of the next iteration, and only if it's still not true at that point. If you want the loop condition to be tested in the middle of the loop, you need to manually test it with something like your if statement, or you need to reorganize your loop.