set的特性和基本用法——python3.6

Posted 2020-10-14 GraceZen

 

• 特性
  • 无序，不重复的数据组合，用{}表示，eg:{1,2,3,4,5,6}
• 用途
  • 去重，把一个列表变成集合，就自动去重了
  • 关系测试，测试两组数据之间的交集，差集，并集，对称差集，包含（子集和超集，相交和不相交）关系
• 基本语法
  • set()：创建一个空集合，用set（）创建，不能直接用s = {}，这是创建一个空字典
  • 

    s = set()
    print(type(s))    # =><class ‘set‘>

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  • add：往集合中添加一个元素，如果添加的元素集合中已有，则集合没有任何变化，只能添加不可变数据
  • 

    s = {1,2,3,4,5}
    s.add(1)
    print(s)    # =>{1, 2, 3, 4, 5}
    s.add(6)
    print(s)    # =>{1, 2, 3, 4, 5, 6}

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  • update：往集合中添加多个元素，自动去重
  • 

    s = {1,2,3,4,5}
    s.update({1,2,6,7,8})
    print(s)    # =>{1, 2, 3, 4, 5, 6, 7, 8}

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  • discard：删除指定元素，如果要删除的元素集合中不存在，do nothing
  • 

    s = {1,2,3,4,5}
    s.discard(1)
    print(s)    # =>{2, 3, 4, 5}

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  • remove：删除指定元素，如果要删除的元素集合中不存在，报错
  • 

    s = {1,2,3,4,5}
    s.remove(1)
    print(s)    # =>{2, 3, 4, 5}
    s.remove(6) # =>报错

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  • pop：随机删除一个元素，无序的，当集合为空时，报错
  • 

    s = {1,2}
    s.pop()
    print(s)    # =>{2}
    s.pop()
    s.pop()     # =>报错

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  • clear：清空
  • 

    s = {1,2,3,4,5}
    s.clear()
    print(s)    # =>set()

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  • copy：浅复制
  • 

    s = {1,2,3,4,5}
    s1 = s.copy()
    print(s1)   # =>{1,2, 3, 4, 5}

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  • difference：差集，差集后的结果是一个新的集合

  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s3 = s1.difference(s2)
    print(s3)   # =>{1, 2, 3}
    s3 = s1-s2
    print(s3)   # =>{1, 2, 3}
    s4 = s2.difference(s1)
    print(s4)   # =>{8, 6, 7}
    s4 = s2-s1
    print(s4)   # =>{8, 6, 7}

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  • difference_update：删除s1集合中含有s2集合中的元素，并返回给s1

  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s3 = s1.difference_update(s2)
    print(s1)   # =>{1, 2, 3}

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  • intersection：交集，交集后的结果是一个新的集合

  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s3 = s1.intersection(s2)
    print(s3)   # =>{4, 5}
    s3 = s1 & s2
    print(s3)   # =>{4, 5}
    s3 = s2.intersection(s1)
    print(s3)   # =>{4, 5}
    s3 = s2 & s1
    print(s3)   # =>{4, 5}

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  • intersection_update：将s1和s2的交集更新给s1

  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s1.intersection_update(s2)
    print(s1)   # =>{4, 5}

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  •  union：并集

  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s3 = s1.union(s2)
    print(s3)   # =>{1, 2, 3, 4, 5, 6, 7, 8}
    s3 = s1 | s2
    print(s3)   # =>{1, 2, 3, 4, 5, 6, 7, 8}

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  • isdisjoint：判断两个集合是否有交集，如果没有，返回True，如果有，返回False

  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s3 = {8,9}
    print(s1.isdisjoint(s2))   # => False
    print(s1.isdisjoint(s3))   # =>True

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  • issubset：判断s2是否是s1的子集，如果是，则True，or，False

    

    s1 = {1,2,3,4,5}
    s2 = {4,5}
    print(s2.issubset(s1))   # =>True

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  • issupper：判断s1是否是s2的超集
  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5}
    print(s1.issuperset(s2))   # =>True

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  • symmetric_difference：对称差集
  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s3 = s1.symmetric_difference(s2)
    print(s3)   # =>{1, 2, 3, 6, 7, 8}
    s3 = s2.symmetric_difference(s1)
    print(s3)   # =>{1, 2, 3, 6, 7, 8}

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  • symmetric_difference_updata：将对称差集更新给s1，或者s2
  • 

    s1 = {1,2,3,4,5}
    s2 = {4,5,6,7,8}
    s1.symmetric_difference_update(s2)
    print(s1)   # =>{1, 2, 3, 6, 7, 8}
    s2.symmetric_difference_update(s1)
    print(s2)   # =>{1, 2, 3, 4, 5}

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• 其他用法：
  • in ，not in 判断某元素是否在集合内
  • == ，!=判断两个集合是否相等