Python set type operations and intersection-Python Tutorial-php.cn

Python set type operations and intersection

高洛峰

Release： 2017-03-01 13:56:04

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Reading Contents

•Introduction
•Basic Operations
•Function Operations

Introduction

Python's set is an unordered set of non-repeating elements. Its basic functions include relationship testing and elimination of duplicate elements. Set objects also support union, intersection, difference, symmetric difference, etc.

sets supports x in set, len(set), and for x in set. As an unordered collection, sets do not record element positions or insertion points. Therefore, sets do not support indexing, slicing, or other sequence-like operations.

Basic operations

>>> x = set("jihite")
>>> y = set([&#39;d&#39;, &#39;i&#39;, &#39;m&#39;, &#39;i&#39;, &#39;t&#39;, &#39;e&#39;])
>>> x    #把字符串转化为set，去重了
set([&#39;i&#39;, &#39;h&#39;, &#39;j&#39;, &#39;e&#39;, &#39;t&#39;])
>>> y
set([&#39;i&#39;, &#39;e&#39;, &#39;m&#39;, &#39;d&#39;, &#39;t&#39;])
>>> x & y  #交
set([&#39;i&#39;, &#39;e&#39;, &#39;t&#39;])
>>> x | y  #并
set([&#39;e&#39;, &#39;d&#39;, &#39;i&#39;, &#39;h&#39;, &#39;j&#39;, &#39;m&#39;, &#39;t&#39;])
>>> x - y  #差
set([&#39;h&#39;, &#39;j&#39;])
>>> y - x
set([&#39;m&#39;, &#39;d&#39;])
>>> x ^ y  #对称差：x和y的交集减去并集
set([&#39;d&#39;, &#39;h&#39;, &#39;j&#39;, &#39;m&#39;])

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Function operations

>>> x
set([&#39;i&#39;, &#39;h&#39;, &#39;j&#39;, &#39;e&#39;, &#39;t&#39;])
>>> s = set("hi")
>>> s
set([&#39;i&#39;, &#39;h&#39;])
>>> len(x)          #长度

>>> &#39;i&#39; in x
True
>>> s.issubset(x)       #s是否为x的子集
True
>>> y
set([&#39;i&#39;, &#39;e&#39;, &#39;m&#39;, &#39;d&#39;, &#39;t&#39;])
>>> x.union(y)        #交
set([&#39;e&#39;, &#39;d&#39;, &#39;i&#39;, &#39;h&#39;, &#39;j&#39;, &#39;m&#39;, &#39;t&#39;])
>>> x.intersection(y)     #并
set([&#39;i&#39;, &#39;e&#39;, &#39;t&#39;])
>>> x.difference(y)      #差
set([&#39;h&#39;, &#39;j&#39;])
>>> x.symmetric_difference(y) #对称差
set([&#39;d&#39;, &#39;h&#39;, &#39;j&#39;, &#39;m&#39;])
>>> s.update(x)        #更新s，加上x中的元素
>>> s
set([&#39;e&#39;, &#39;t&#39;, &#39;i&#39;, &#39;h&#39;, &#39;j&#39;])
>>> s.add(1)         #增加元素
>>> s
set([1, &#39;e&#39;, &#39;t&#39;, &#39;i&#39;, &#39;h&#39;, &#39;j&#39;])
>>> s.remove(1)        #删除已有元素，如果没有会返回异常
>>> s
set([&#39;e&#39;, &#39;t&#39;, &#39;i&#39;, &#39;h&#39;, &#39;j&#39;])
>>> s.remove(2)

Traceback (most recent call last):
 File "<pyshell#29>", line 1, in <module>
  s.remove(2)
KeyError: 2
>>> s.discard(2)        #如果存在元素，就删除；没有不报异常
>>> s
set([&#39;e&#39;, &#39;t&#39;, &#39;i&#39;, &#39;h&#39;, &#39;j&#39;])
>>> s.clear()         #清除set
>>> s
set([])
>>> x
set([&#39;i&#39;, &#39;h&#39;, &#39;j&#39;, &#39;e&#39;, &#39;t&#39;])
>>> x.pop()          #随机删除一元素
&#39;i&#39;
>>> x
set([&#39;h&#39;, &#39;j&#39;, &#39;e&#39;, &#39;t&#39;])
>>> x.pop()
&#39;h&#39;

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