list

Posted 2020-06-13

list是一种有序的集合（或称作列表），可以很方便地添加和删除其中的元素

1 >>> classmates = [‘Michael‘, ‘Bob‘, ‘Tracy‘]

 

可通过序号访问各元素，序号范围：-n ~ n-1，当索引超出了范围时，Python会报一个IndexError错误，序号-1 相当于n-1，-2相当于n-2，-n相当于n-n=0

1 >>> classmates[-1]
2 ‘Tracy‘
3 >>> classmates[2]
4 ‘Tracy‘

1 >>> classmates = [‘Michael‘, ‘Bob‘, ‘Tracy‘]
2 >>> classmates[-10]
3 Traceback (most recent call last):
4   File "<pyshell#11>", line 1, in <module>
5     classmates[-10]
6 IndexError: list index out of range

 

append(...)新增元素：classmates.append(‘Miranda‘)

insert(... , ...)插入元素到指定位置：classmates.insert(2,‘John‘)        第一个参数是序号，不是第几个

1 >>> classmates.append(‘Miranda‘)
2 >>> classmates
3 [‘Michael‘, ‘Bob‘, ‘Tracy‘, ‘Miranda‘]
4 >>> classmates.insert(2,‘John‘)
5 >>> classmates
6 [‘Michael‘, ‘Bob‘, ‘John‘, ‘Tracy‘, ‘Miranda‘]

 

pop()删除末尾元素：classmates.pop()

pop(...)删除指定位置的元素：classmates.pop(1)                              第一个参数是序号，不是第几个

1 >>> classmates.pop()
2 ‘Miranda‘
3 >>> classmates.pop(1)
4 ‘Bob‘
5 >>> classmates
6 [‘Michael‘, ‘John‘, ‘Tracy‘]

 

remove(...)删除指定值第一次出现的位置所在元素：classmates.remove(‘Bob‘)

count(...)统计指定值出现的次数：classmates.count(‘Bob‘)

1 >>> classmates
2 [‘Michael‘, ‘Bob‘, ‘Tracy‘, ‘Bob‘]
3 >>> classmates.remove(‘Bob‘)
4 >>> classmates
5 [‘Michael‘, ‘Tracy‘, ‘Bob‘]
6 >>> classmates.count(‘Bob‘)
7 1

 

1 >>> classmates
2 [‘Michael‘, ‘Tracy‘, ‘Bob‘]
3 >>> len(classmates)
4 3
5 >>> classmates+[‘John‘]
6 [‘Michael‘, ‘Tracy‘, ‘Bob‘, ‘John‘]
7 >>> [‘hhh‘]*5
8 [‘hhh‘, ‘hhh‘, ‘hhh‘, ‘hhh‘, ‘hhh‘]

 

不能将一个列表和一个字符串合并到一起，除非先把列表转化为字符串，或者把字符串转化为列表                list的元素的数据类型可以不同

1 >>> str([1,2])+"34"             #same as "[1,2]"+"34"
2 ‘[1, 2]34‘
3 >>> [1,2]+list("34")            #same as [1,2]+[‘3‘,‘4‘]
4 [1, 2, ‘3‘, ‘4‘] 

 

1 >>> 3 in [1,2,3]
2 True
3 >>> for x in [1,2,3]:
4     print(x,end=‘#‘)
5 
6     
7 1#2#3#

 

>>> res=[x*3 for x in ‘hello‘]
>>> res
[‘hhh‘, ‘eee‘, ‘lll‘, ‘lll‘, ‘ooo‘]
>>> res=[]
>>> for x in ‘hello‘:
    res.append(x*3)

    
>>> res
[‘hhh‘, ‘eee‘, ‘lll‘, ‘lll‘, ‘ooo‘]

 

list元素也可以是另一个list

1 >>> s = [‘python‘, ‘java‘, [‘asp‘, ‘php‘], ‘scheme‘]
2 
3 >>> len(s)
4 4
5 
6 >>> s[2][1]
7 ‘asp‘

 

>>> kk=[1,2,3,4,5,6]
>>> kk[-5]
2
>>> kk[-5:-2]      #包含前一个序号的元素，不包含后一个
[2, 3, 4]
>>> kk[1:4]        #相当于kk[1:4]
[2, 3, 4]

>>> kk[1:]              #从序号1一直到最后
[2, 3, 4, 5, 6]

 

 1 >>> matrix=[[1,2,3],[4,5,6],[7,8,9]]
 2 >>> matrix[1]
 3 [4, 5, 6]
 4 >>> matrix[1][1]
 5 5
 6 
 7 >>> matrix=[[1,2,3],
 8             [4,5,6],
 9             [7,8,9]]
10 >>> matrix[1]
11 [4, 5, 6]
12 >>> matrix[1][1]
13 5

 

 1 >>> kk=[1,2,3,4]
 2 >>> kk[1]=7
 3 >>> kk
 4 [1, 7, 3, 4]
 5 >>> kk[1:3]=[8,9]
 6 >>> kk
 7 [1, 8, 9, 4]
 8 >>> kk[1:2]=[10,11,12]    #长度不一定要一样
 9 >>> kk
10 [1, 10, 11, 12, 9, 4]

 

 1 >>> kk=[1,2]
 2 >>> kk.extend([3,4,5])
 3 >>> kk
 4 [1, 2, 3, 4, 5]
 5 >>> kk.index(3)       #显示括号里元素的序号
 6 2
 7 >>> del kk[2]
 8 >>> kk
 9 [1, 2, 4, 5]
10 >>> del kk[1:3]
11 >>> kk
12 [1, 5]

 

1 >>> kk=[1,2,3,4,5]
2 >>> kk[1:]=[]
3 >>> kk
4 [1]
5 >>> kk=[1,2,3,4,5]
6 >>> kk[1]=[]
7 >>> kk
8 [1, [], 3, 4, 5]