005 列表的基本使用

• 简单地说，列表就是一组有顺序的数据的组合

创建

例1

>>> a = []
>>> a
[]
>>> type(a)
<class 'list'>
>>> 
>>> b = list()
>>> b
[]
>>> type(b)
<class 'list'>
>>> 

例2

>>> a = [100]
>>> a
[100]
>>> type(a)
<class 'list'>
>>> 
>>> b = [1, 2, 3, 4, 5]
>>> b
[1, 2, 3, 4, 5]
>>> type(b)
<class 'list'>
>>> 

常用操作

• 访问：索引从 0 开始
• 分片/切片：截取列表的一部分或全部，索引左闭右开

访问

例3

>>> a = [0, 1, 2, 3, 4]
>>> a[0]
0
>>> a[2]
2
>>> a[-1]
4
>>> a[5]
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    a[5]
IndexError: list index out of range
>>> 

分片

例4

>>> a = [0, 1, 2, 3, 4]
>>> a[1:4]  # [1, 4)
[1, 2, 3]
>>> a[-4:-1]
[1, 2, 3]
>>> a[-1:-4]
[]
>>> a[:]
[0, 1, 2, 3, 4]
>>> a[:5]  # 前 5 个
[0, 1, 2, 3, 4]
>>> a[3:]  # 除前 3 个
[3, 4]
>>> a[3:10]  # 分片时索引可以超出范围
[3, 4]
>>> a[-10:]
[0, 1, 2, 3, 4]
>>> 

例5

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> a[2:8:1]
[2, 3, 4, 5, 6, 7]
>>> a[2:8:2]
[2, 4, 6]
>>> 
>>> a[2:8:0]
Traceback (most recent call last):
  File "<pyshell#5>", line 1, in <module>
    a[2:8:0]
ValueError: slice step cannot be zero
>>> 

例6

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> a[6:2:-1]
[6, 5, 4, 3]
>>> a[-1:-5:-1]
[9, 8, 7, 6]
>>> 

id()

• id(): 显示一个变量或者数据的”身份证“

例7

>>> a = 100
>>> b = 200
>>> id(a)
140709107680128
>>> id(b)
140709107683328
>>> 

例8

>>> a = 100
>>> b = a
>>> id(a)
140709107680128
>>> id(b)
140709107680128
>>> 

例9

>>> a = [1, 2, 3, 4, 5]
>>> b = a  # 合用一份数据
>>> c = a[:]  # 新生成一份数据
>>> id(a)
2186608330432
>>> id(b)
2186608330432
>>> id(c)
2186608329792
>>> 
>>> a[0] = 100
>>> a
[100, 2, 3, 4, 5]
>>> b
[100, 2, 3, 4, 5]
>>> c
[1, 2, 3, 4, 5]
>>>