为什么我的try-except块卡在了循环中？

Question

I am trying to catch an Index out of range error with the following try and except block.

def getStepList(r, h, d):
    x = len(r)-1
    y = len(h)-1
    list = []
    while True:
        try:
            if x == 0 and y == 0: 
                break
            elif x >= 1 and y >= 1 and d[x][y] == d[x-1][y-1] and r[x-1] == h[y-1]:
                x = x - 1
                y = y - 1
            elif y >= 1 and d[x][y] == d[x][y-1]+1:
                #insertion
                x = x
                y = y - 1
                list.append(h[y])
                print('insertion')

            elif x >= 1 and y >= 1 and d[x][y] == d[x-1][y-1]+1:
                #substitution
                x = x - 1
                y = y - 1
                list.append(r[x])
                print('substitution')

            else:
                #deletion
                x = x - 1
                y = y
                list.append(r[x])
                print('deletion')

        except IndexError:
            print('index error')

    return list[::-1]

but it gets stuck in a infinite loop. I want it to ignore it and proceed appending the next instances. (For reference its a piece of code that uses a metric of another function to determine which words were inserted, substituted or deleted at each operation).

I feel like I should know this, but in all honesty I am stuck.

Answer 1

Don't do a while True. Change your while condition to:

while(not (x == 0 and y == 0)):

Inside your exception also add a break

except IndexError:
     print('index error')
     break

You could also add some checks to see what the specific Index Error might be:

d_len = len(d)
r_len = len(r)
h_len = len(h)
d_x_of_y_len = len(d[x][y])
if(x > d_len):
    print("x is too big")
if(y > d_x_of_y_len):
    print("y is too big")