Python set 拾遗

• 初始化

s = set('abc') # {'a', 'b', 'c'}
print(s)
s = set(['a', 'b', 'c']) # {'a', 'b', 'c'}
print(s)

• add()添加

s = set(['a', 'b', 'c'])
print(s)

s.add('e')
print(s) # {'a', 'e', 'c', 'b'}

• clear()清除
• discard()删除
• remove删除（当要删除的元素不存在时，抛出异常）
• pop() 随机删除一个元素（当集合为空时，抛出异常）

s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s.discard('e')           # {'b', 'a', 'c'}
print(s)
s.discard('a')           # {'b', 'c'}
print(s)

s.remove('b')           # {'c'}
print(s)

s.remove('e')           # raise KeyError: 'e'

s.clear()  # set()
print(s)



s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)

print(s.pop())            # 随机
print(s)
s.pop()
s.pop()
print(s)                  # set()
s.pop()                   # KeyError: 'pop from an empty set'

• copy()复制

s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2 = s.copy()  # {'c', 'b', 'a'}
print(s2)

• difference()差
• difference_update()用差更新集合
• symmetric_difference() 对称差
• symmetric_difference_update() 用对称差更新（只剩除了交集的了）

s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2 = set('bcef')          # {'b', 'e', 'c', 'f'}
print(s2)
print(s2.difference(s))   # {'e', 'f'}
print(s.difference(s2))   # {'a'}



s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2 = set('bcef')          # {'b', 'e', 'c', 'f'}
print(s2)
s.difference_update(s2)   # {'a'}
print(s)
s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2.difference_update(s)  # {'e', 'f'}
print(s2)



s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2 = set('bcef')          # {'b', 'e', 'c', 'f'}
print(s2)

print(s.symmetric_difference(s2))   # {'e', 'f', 'a'}
s.symmetric_difference_update(s2)   # {'e', 'f', 'a'}
print(s)

• intersection()交集

s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2 = set('bcef')          # {'b', 'e', 'c', 'f'}
print(s2)
print(s.intersection(s2)) # {'b', 'c'}
print(s2.intersection(s)) # {'b', 'c'}


print(s)                  # {'c', 'b', 'a'}
print(s2)                 # {'c', 'f', 'b', 'e'}
s.intersection_update(s2) 
print(s)                  # {'c', 'b'}

• isdisjoint()判断是否相交
• issubset() 判断是否是子集
• issuperset() 判断是否是父集

s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2 = set('bcef')          # {'b', 'e', 'c', 'f'}
print(s2)
s3 = set('gh')          # {'g', 'h'}
print(s3)
print(s.isdisjoint(s2)) # False
print(s.isdisjoint(s3)) # True
s4 = set('abcd')          # {'b', 'c', 'd', 'a'}
print(s4)
print(s.issubset(s2))     # False
print(s.issubset(s4))     # True

print(s.issuperset(s4))     # False
print(s4.issuperset(s))   # True

• union() 并集
• update() 用并集更新

s = set(['a', 'b', 'c'])  # {'b', 'a', 'c'}
print(s)
s2 = set('bcef')          # {'b', 'e', 'c', 'f'}
print(s2)
print(s.union(s2))        # {'c', 'a', 'f', 'b', 'e'}


s.update(s2)              # {'c', 'a', 'f', 'b', 'e'}
print(s)