python集合(set)的运算

1.交集

In [1]: a = {1,2,3,4}

In [2]: b = {3,4,5,6}

In [3]: a & b
Out[3]: {3, 4}

In [4]: a.intersection(b)
Out[4]: {3, 4}

2.并集

In [5]: a | b
Out[5]: {1, 2, 3, 4, 5, 6}

In [6]: a.union(b)
Out[6]: {1, 2, 3, 4, 5, 6}

3.差集

In [9]: a-b
Out[9]: {1, 2}

In [10]: b-a
Out[10]: {5, 6}

In [11]: a.difference(b)
Out[11]: {1, 2}

In [12]: b.difference(a)
Out[12]: {5, 6}

4.对称差集

In [13]: a^b
Out[13]: {1, 2, 5, 6}

In [14]: a.symmetric_difference(b)
Out[14]: {1, 2, 5, 6}

5.集合的子集和超集

In [15]: x = {1,2,3,4}

In [16]: y = {1,2,3}

In [17]: y.issubset(x)
Out[17]: True

In [18]: x.issuperset(y)
Out[18]: True

下面的图片形象地展示了set集合的各种运算：

集合 x <==> ① + ②

集合 x <==> ② + ③

交集 x&6 <==> ②

并集 x|y <==> ① + ② + ③

差集 x-y <==> ①

差集 y-x <==> ③

对称差集 x^y == y^x 　<==> ① + ③