tang=0
while tang<10:
    print(tang)
    tang += 1

0
1
2
3
4
5
6
7
8
9

tangs=set(['tang','yu','di'])
while tangs:
    tang=tangs.pop()
    print(tang)　

yu
di
tang

tang=set(['tang','yu','di'])
for name in tang:
    print(name)

yu
di
tang