一文看懂Python中的集合运算&，|，

关于集合的概念

Python 中常用的集合方法是执行标准的数学运算，例如：求并集、交集、差集以及对称差。下图显示了一些在集合 A 和集合 B 上进行的标准数学运算。每个韦恩（Venn）图中的红色部分是给定集合运算得到的结果。

Python中相应符号：

• &符号在Python中既可以执行通常的按位与运算，也可以执行set集合里面的交集运算
• |：并集；也可以表示数字运算中的按位或运算
• -：差集
• ^：对称差集

举例

pre = ["berry","grape","pea_r","apple","banana","pear"]
pos = ["apple","banana","pear","potato","cucumber"]
pre_set = set(pre)  # 转换list为集合set
pos_set = set(pos)

union = pos_set | pre_set  # 并集
print('The union of the two sets above is:\n{}\n'.format(union))

intersection = pos_set & pre_set  # 交集
print('The intersection of two sets is:\n{}\n'.format(intersection))

only_in_preset = pre_set - pos_set  # 差集
print('The unique part in pre_set is:\n{}\n'.format(only_in_preset))

only_in_posset = pos_set - pre_set  # 差集
print('The unique part in pos_set is:\n{}\n'.format(only_in_posset))

sym_set_diff = pos_set^pre_set      # 对称差集
print('The symmetric set difference of the two sets is:\n{}'.format(sym_set_diff))

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输出结果如下：

The union of the two sets above is:
{'potato', 'grape', 'banana', 'pear', 'berry', 'pea_r', 'cucumber', 'apple'}

The intersection of two sets is:
{'pear', 'apple', 'banana'}

The unique part in pre_set is:
{'berry', 'grape', 'pea_r'}

The unique part in pos_set is:
{'potato', 'cucumber'}

The symmetric set difference of the two sets is:
{'potato', 'pea_r', 'berry', 'cucumber', 'grape'}

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