<reponame>pylangstudy/201708
s = set([1,2,3,2,1]);
print(s, type(s), len(s))
s = frozenset([1,2,3,2,1]);
print(s, type(s), len(s))

s = set([1,2,3,2,1]);
print(s, type(s), len(s))
s = frozenset([1,2,3,2,1]);
print(s, type(s), len(s))