运行提示列表索引超范围 ，但是我没看出来为什么超范围。求助

[王半疯]

a = []
for i in range(10):
a.append([])
for j in range(i + 1):
a[i].append([1] if j == 0 or j == i else [])
for i in a:
print(i)
for i in range(2,10):
for j in range(1,i):
a[i][j] = sum(a[i-1][j-1], [i-1][j])
for i in a:
print(i)

python 3.6 版本，打印杨辉三角形。
运行提示列表索引超范围 ，但是我没看出来为什么超范围。求助

[王半疯]

a = [] for i in range(10): a.append([]) for j in range(i + 1): a[i].append([1] if j == 0 or j == i else []) for i in a: print(i) for i in range(2,10): for j in range(1,i): a[i][j] = sum(a[i-1][j-1], a[i-1][j]) for i in a: print(i) 粘的时候不小心删掉了一个a，

[王半疯]

a = [] for i in range(10): a.append([]) for j in range(i + 1): a[i].append(1 if j == 0 or j == i else 0) for i in a: print(i) for i in range(2, 10): for j in range(1, i): a[i][j] = a[i - 1][j - 1] + a[i - 1][j] for i in a: print(i)

[chuifengde]

def res(n):
    if n < 3:return [1] * n
    s = res(n-1)
    return [1] + [s[_] + s[_+1] for _ in range(n-2)] + [1]

for _ in range(1, 11):
    print( res(_))