标签：set
一、集合
1、集合的定义
In [74]: s = {}
In [74]: s = {} # 空大括号是空的字典
In [75]: type(s)
Out[75]: dict
In [77]: type(s)
Out[77]: set
In [78]: help(set)
Help on class set in module builtins:
class set(object)
| set() -> new empty set object
| set(iterable) -> new set object
|
| Build an unordered collection of unique elements.
|
| Methods defined here:
In [80]: s = set([1, 2])
In [81]: s
Out[81]: {1, 2}
In [82]: s = set("xxj")
In [83]: s
Out[83]: {‘j‘, ‘x‘}
In [84]: s = {1, 2, 1, 3}
In [85]: s
Out[85]: {1, 2, 3} 集合是无序的，元素不能重复，元素要能被哈希（hash，不可变）
二、集合的操作
1、增
z## set.add()
In [86]: s
Out[86]: {1, 2, 3}
In [87]: s.add("a") # 原地增加单个元素，元素要可哈希
In [88]: s
Out[88]: {1, 2, 3, ‘a‘}
In [89]: s.add(3)
In [90]: s
Out[90]: {1, 2, 3, ‘a‘}
In [93]: s.add([1, 2])
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-93-2beaf0c16593> in <module>()
----> 1 s.add([1, 2])
TypeError: unhashable type: ‘list‘
In [94]: help(s.add)
In [95]: s.add((1, 2))
In [96]: s
Out[96]: {(1, 2), 1, 2, 3, ‘a‘}
## set.update() # 原地增加可迭代对象的元素
In [99]: help(s.update)
Help on built-in function update:
update(...) method of builtins.set instance
Update a set with the union of itself and others.
In [127]: s = set()
In [128]: s
Out[128]: set()
In [129]: type(s)
Out[129]: set
In [101]: s.update(10)
-----------------------------------------------------------------------
TypeError Traceback (most recent call l
<ipython-input-101-c184888ad9c5> in <module>()
----> 1 s.update(10)
TypeError: ‘int‘ object is not iterable
In [131]: s.update(["a"])
In [132]: s
Out[132]: {‘a‘}
In [133]: s.update(["a"], ["b"])
In [134]: s
Out[134]: {‘a‘, ‘b‘}
In [135]: s.update(["a"], ["b"], 1)
-----------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-135-fc556b8d9726> in <module>()
----> 1 s.update(["a"], ["b"], 1)
TypeError: ‘int‘ object is not iterable
In [136]: s.update(["a"], ["b"], "xj")
In [137]: s
Out[137]: {‘a‘, ‘b‘, ‘j‘, ‘x‘}
In [139]: s.update([["S", "B"]])
-----------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-139-da563f39a191> in <module>()
----> 1 s.update([["S", "B"]])
TypeError: unhashable type: ‘list‘2、删
## set.remove()
In [142]: s
Out[142]: {‘a‘, ‘b‘, ‘j‘, ‘x‘}
In [143]: s.remove("a")
In [144]: s
Out[144]: {‘b‘, ‘j‘, ‘x‘}
In [151]: s.remove("S")
-----------------------------------------------------------------------
KeyError Traceback (most recent call last)
<ipython-input-151-332efdd48daa> in <module>()
----> 1 s.remove("S")
KeyError: ‘S‘
## set.pop()
In [153]: s = {1, 2, 3, 4}
In [154]: s.pop()
Out[154]: 1
In [155]: s
Out[155]: {2, 3, 4}
In [156]: s.pop(5)
-----------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-156-23a1c03efc29> in <module>()
----> 1 s.pop(5)
TypeError: pop() takes no arguments (1 given)
In [157]: s.pop()
Out[157]: 2
In [158]: s.pop()
Out[158]: 3
In [159]: s.pop()
Out[159]: 4
In [160]: s.pop()
-----------------------------------------------------------------------
KeyError Traceback (most recent call last)
<ipython-input-160-e76f41daca5e> in <module>()
----> 1 s.pop()
KeyError: ‘pop from an empty set‘
## set.discard()
In [165]: help(set.discard)
Help on method_descriptor:
discard(...)
Remove an element from a set if it is a member.
If the element is not a member, do nothing.
In [166]: s = {1, 2, 3}
In [167]: s.discard(2)
In [168]: s.discard(1, 3)
-----------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-168-8702b734cbc4> in <module>()
----> 1 s.discard(1, 3)
TypeError: discard() takes exactly one argument (2 given)
In [169]: s.discard(2) # 元素不存在时，不会报错
In [170]: s
Out[170]: {1, 3}
In [32]: s.clear()
In [33]: s
Out[33]: set()
In [47]: del(s)
In [48]: s
-----------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-48-f4d5d0c0671b> in <module>()
----> 1 s
NameError: name ‘s‘ is not defined小结：
remove 删除给定的元素，元素不存在时，抛出KeyError
discard 删除给定的元素，元素不存在时，什么也不做
pop 随机删除一个元素并返回，集合为空返回KeyError，
clear 清空集合
3、改
set不能修改单个元素
4、查找
集合不能通过索引，集合不是线性结构，没有索引
集合没有访问单个元素的方法
集合没有查找的方法
做成员运算（in和not in）的时候，set的效率远高于list（O(1)和O(n)）;
O(n)不一定小于O(1)，还需要看数据规模
三、集合的集合操作
标签：set
原文地址：http://xiexiaojun.blog.51cto.com/2305291/1932019
