there's no next() function in a yield generator in python 3

In this question, I have an endless sequence using Python generators. But the same code doesn't work in Python 3 because it seems there is no next() function. What is the equivalent for the next function?

def updown(n):
    while True:
        for i in range(n):
            yield i
        for i in range(n - 2, 0, -1):
            yield i

uptofive = updown(6)
for i in range(20):
    print(uptofive.next())