006 列表的常用方法

查看

• dir(list): 列出 list 的方法
• help(list): 查看开发者对 list 方法所编写的详细描述文档
  • help(list.append) 可以仅查看 append() 的用法

append()

>>> a = [0, 1, 2, 3]
>>> a.append(4)
>>> a
[0, 1, 2, 3, 4]
>>> a.append(5, 6)
Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    a.append(5, 6)
TypeError: append() takes exactly one argument (2 given)
>>> 

说明

• 在原列表的基础上直接操作
• append() 会返回一个 None
• append() 仅能在列表末尾追加一个数据，多加报错

extend()

>>> a = [0, 1, 2, 3]
>>> a.extend(4)
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    a.extend(4)
TypeError: 'int' object is not iterable
>>> a.extend([4])
>>> a
[0, 1, 2, 3, 4]
>>> a.extend([5, 6])
>>> a
[0, 1, 2, 3, 4, 5, 6]
>>> a.extend("york")
[0, 1, 2, 3, 4, 5, 6, 'y', 'o', 'r', 'k']
>>> 

说明

• 在原列表的基础上直接操作
• extend() 是向列表追加一个可迭代的数据

insert()

>>> a = [0, 1, 2, 3]
>>> a.insert(3, "York")
>>> a
[0, 1, 2, 'York', 3]
>>> a.insert(10, "Fish")  # 索引超标，当作 append()
>>> a
[0, 1, 2, 'York', 3, 'Fish']
>>> 

说明

• 在原列表的基础上直接操作
• insert() 与插队一个效果，就是把目标值插到目标索引

index: 0 1 2  3 4
num:   9 8 7  5 4    a.insert(3, 66)
            /       => 9 8 7 66 5 4
            66

---

pop()

>>> a = [0, 1, 2, 3]
>>> a.pop()  # 弹末尾
3
>>> a
[0, 1, 2]
>>> a.pop(0)  # 按索引弹
0
>>> a
[1, 2]
>>> a.pop(10)  # 索引超标，抛出异常
Traceback (most recent call last):
  File "<pyshell#5>", line 1, in <module>
    a.pop(10)
IndexError: pop index out of range
>>> 

说明

• 在原列表的基础上直接操作

remove()

>>> a = [1, 2, 3, 2, 1]
>>> a.remove(2)
>>> a
[1, 3, 2, 1]
>>> a.remove(10)
Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    a.remove(10)
ValueError: list.remove(x): x not in list
>>> 

说明

• 在原列表的基础上直接操作
• 从头遍历，移除第一个
• 没有找到，抛出异常

clear()

>>> a = [0, 1, 2, 3]
>>> a.clear()
>>> a
[]
>>> 

del

>>> a = [0, 1, 2, 3]
>>> del a
>>> a
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    a
NameError: name 'a' is not defined
>>> 

---

reverse()

>>> a = [0, 1, 2, 3]
>>> a.reverse()
>>> a
[3, 2, 1, 0]
>>> 

sort()

>>> a = [1, 3, 5, 2, 4, 6]
>>> a.sort()
>>> a
[1, 2, 3, 4, 5, 6]
>>> a.sort(reverse=True)
>>> a
[6, 5, 4, 3, 2, 1]
>>> 

---

count()

>>> a = [1, 2, 3, 2, 1]
>>> a.count(1)
2
>>> 

len()

>>> a = [1, 2, 3, 4, 5]
>>> len(a)
5
>>> 

说明

• len(list) 是 O(1) 的，不像 C 那样每次都要重新遍历，因为 list 有块记录长度的空间

index()

>>> a = ['1', '2', '3', '2', '1']
>>> a.index('2')
1
>>> a.index('2', 2)
3
>>> a.index('5')
Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    a.index('5')
ValueError: '5' is not in list
>>> 

copy()

>>> a = [0, 1, 2, 3]
>>> b = a.copy()
>>> id(a)
2113228704064
>>> id(b)
2113228640128
>>> a[0] = 10
>>> a
[10, 1, 2, 3]
>>> b
[0, 1, 2, 3]
>>> 
>>> c = [0, 1, [2, 3]]
>>> d = a.copy()
>>> c[2][0] = 20
>>> c
[0, 1, [20, 3]]
>>> d
[0, 1, [20, 3]]
>>> 

说明

• copy() 只能管第一层
• 若想“深拷贝”，需要 from copy import deepcopy, b = deepcopy(a)