Python for循环enumerate

a = [1, 2, 3, 4, 5]
print(a)

def foo(item):
    for i, x in enumerate(item):
        item[i] = x*x
    return item

print(foo(a))

输出：

[1, 2, 3, 4, 5]
[1, 4, 9, 16, 25]