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. 5 .7 six data types Five: Sets ( set)
Collection (set) is a set of unordered elements will not be repeated. By definition, we can get the following three sets of characteristics:
Features a: Element not allowed to repeat , if you enter repeating elements in the initialization list, Python will automatically duplicate elements removed, leaving only a
Features 2: element no particular order, a set of the same elements when used repeatedly arranged in the original order are not necessarily
Features 3: Caucasus can not lead to access specific elements, but can traverse all the elements in a for loop
Braces may be used or set () function creates a set collection Note: Creating a empty set must be set () instead of {}
If the individual is a [braces {} is an empty dictionary]
# 举例1：
>>> s = {1,2,3,1,3,4,5}
>>> print(s)
{1, 2, 3, 4, 5} #Python会自动将重复的元素去掉，只保留一个
>>> print(s[0]) #报错，因为集合中的元素不能加索引
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'set' object does not support indexing
() Function is used to add an element to the collection add. Note: because the elements in the set is unordered, and therefore the position of the additive element is not determined
# 举例2：
>>> t=set() #创建一个空集合
>>> t.add('a') #向集合中添加元素a
>>> print(t)
{'a'}
>>> t.add('b') #向集合中添加元素b
>>> print(t)
{'b', 'a'} #元素b的位置出现在a的前面
>>> t.add('c')
>>> print(t) #向集合中添加元素c
{'b', 'c', 'a'} #元素c的位置在a和b中间，可见集合中元素的位置是不确定的
>>> t.add('a')
>>> print(t) #集合中已有元素a因此不会再次添加元素a
{'b', 'c', 'a'}
Relationship between the elements may be performed by the test set operator and eliminating duplicate entries
# 举例3：
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a
{'r', 'c', 'a', 'd', 'b'} #集合a的元素被Python自动去重
>>> b
{'c', 'a', 'l', 'm', 'z'} #集合b的元素被Python自动去重
# 举例4：
>>> a - b #求a和b的差集
{'d', 'b', 'r'}
>>> a | b #求a和b的并集
{'r', 'c', 'a', 'd', 'b', 'l', 'm', 'z'}
>>> a & b #求a和b的交集
{'c', 'a'}
>>> a ^ b #求a和b中不同时存在的元素
{'r', 'd', 'b', 'l', 'm', 'z'}
Reference Tutorial:
Liao Xuefeng of Python tutorials
https://www.liaoxuefeng.com/wiki/1016959663602400
Liao Xuefeng's Java Tutorial
https://www.liaoxuefeng.com/wiki/1252599548343744
Python3 Tutorial | Tutorial rookie
https://www.runoob.com/python3/
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