集合、序列、字典

集合：

集合用{}或set 创建，空集合一定要用set 创建。

集合的特点：确定、无序、互异

集合应用场景：

数据去重

>>> a=[11,22,33,55,22,11]
>>> b=set(a)
>>> b
{33, 11, 22, 55}
>>> c=list(b)
>>> c
[33, 11, 22, 55]
>>>

包含关系比较

>>> "p" in {"p","y",123}
True
>>> {"p","y"}>={"y","p"}
True
>>> {"p","y"}>={"p","y",123}
False