python遇到IndexError: list index out of range问题，如何解决？

为什么会在代码倒数第二行出现IndexError: list index out of range错误，该如何解决？谢谢大佬

       for x in range(columns):
        for y in range(rows):
            if (BW[y][x] == 255):
                phi = ang[y][x]
                i = round((phi + (math.pi / 2)) / d)
                if (i == 0):
                    i = 1
                v = F[i] + 1
                if (v > s):
                    s = s + 1
                T = [[[0 for j in range(entries)] for j in range(2)] for j in range(s)]
                F[i-1] = F[i-1] + 1
                T[i-1][1][v] = x - xr
                T[i-1][2][v] = y - yr

调试输出下v的值，这里是下标越界，看下v-1是多少，以及t的最后一维的大小