python的set和其他语言类似, 是一个无序不重复元素集, 基本功能包括关系测试和消除重复元素. 集合对象还支持union(联合), intersection(交), difference(差)和sysmmetric difference(对称差集)等数学运算.
sets 支持 x in set, len(set),和 for x in set。作为一个无序的集合，sets不记录元素位置或者插入点。因此，sets不支持 indexing, slicing, 或其它类序列（sequence-like）的操作。
例子：
print('{} a word she can get what she {} for.'.format('with', 'came'))
print('{preposition} a word she can get what she {verb} for.'.format(preposition = 'With', verb = 'came'))
print('{0} a worf she can get what she {1} for.'.format('with', 'came'))
s1 = set(['lk','jim','tom','jim'])
print(s1)#打印会删除重复值
s2 = s1.difference(['xzdz','lk'])
print(s2)#删除列表中的元素，源文件不修改
print(s1)#不变
s1.difference_update(['xzdz','lk'])
print(s1)#源文件修改了
s4 = s1.pop()
print(s4)#被删除的元素
print(s1)#删除元素后
x = set('szxpzm')
y = set(['h','z','m','x'])
print(x&y)#交集
print(x|y)#并集
print(x-y)#差集
print(x,y)
结果：
with a word she can get what she came for.
With a word she can get what she came for.
with a worf she can get what she came for.
{'tom', 'jim', 'lk'}
{'tom', 'jim'}
{'tom', 'jim', 'lk'}
{'tom', 'jim'}
tom
{'jim'}
{'z', 'x', 'm'}
{'x', 'm', 'z', 's', 'p', 'h'}
{'s', 'p'}
{'z', 'x', 's', 'm', 'p'} {'z', 'x', 'm', 'h'}
