1. 集合（set）集合的显著特点是：里面元素无重复
1）set的创建
>>> num2 = {1, 2, 4, 5, 6, 7, 5, 4, 3, 2, 1, 0}
>>> num2
{0, 1, 2, 3, 4, 5, 6, 7}
>>> set1 = set([1, 1, 2, 4, 5, 6])
>>> set1
{1, 2, 4, 5, 6}
2）.add() 将一个参数添加进集合中
>>> num2 = {1, 2, 4, 5, 6, 7, 5, 4, 3, 2, 1, 0}
>>> num2.add(6.2)
>>> num2
{0, 1, 2, 3, 4, 5, 6, 7, 6.2}
3) .remove() 将指定元素从原集合中删除
>>> num2 = {0, 1, 2, 3, 4, 5, 6, 7, 6.2}
>>> num2.remove(6.2)
>>> num2
{0, 1, 2, 3, 4, 5, 6, 7}
4) .frozenset() 冰冻集合，集合不能改变
>>> num4 = frozenset([1, 2, 3, 4, 5, 3, 2, 1])
>>> num4
frozenset({1, 2, 3, 4, 5})
>>> num4.add(0)
Traceback (most recent call last):
File "<pyshell#39>", line 1, in <module>
num4.add(0)
AttributeError: 'frozenset' object has no attribute 'add'
