在python中为for循环变量赋值时的混淆行为

i += 10 i

for i in range(20):
    # generator range(20) assigns numbers from 0 to 19 to i

    i += 10
    # i is now 10 to 29; generator not affected

    print(i)

it = iter(range(20))
while(True):
    i = next(it)
    i += 10
    print(i)

i i += 10

i = next(it)