Python -3-列表和元组

1.用list就可以像修改列表那样修改字符串了

>>> list('Hello')

['H', 'e', 'l', 'l', 'o']

可将任何序列作为list的参数

 

2.列表的基本操作

给元素赋值

>>> x = [1, 1, 1]

>>> x[1] = 2

>>> x

[1, 2, 1]

删除元素

>>> names = ['Alice', 'Beth', 'Cecil', 'Dee-Dee', 'Earl']

>>> del names[2]

>>> names

['Alice', 'Beth', 'Dee-Dee', 'Earl']

给切片赋值

>>> name = list('Perl')

>>> name

['P', 'e', 'r', 'l']

>>> name[2:] = list('ar')

>>> name

['P', 'e', 'a', 'r']

改变长度的赋值也可以

>>> name = list('Perl')

>>> name[1:] = list('ython')

>>> name

['P', 'y', 't', 'h', 'o', 'n']

插入新元素

>>> numbers = [1, 5]

>>> numbers[1:1] = [2, 3, 4]

>>> numbers

[1, 2, 3, 4, 5]

相反，也可以删除

>>> numbers

[1, 2, 3, 4, 5]

>>> numbers[1:4] = []

>>> numbers

[1, 5]

 

3.列表方法

append

>>> lst = [1, 2, 3]

>>> lst.append(4)

>>> lst

[1, 2, 3, 4]

clear

>>> lst = [1, 2, 3]

>>> lst.clear()

>>> lst

【】

copy

常规复制只是将另一个名称关联到列表

>>> a = [1, 2, 3]

>>> b = a

>>> b[1] = 4

>>> a

[1, 4, 3]

copyj将b关联到a的副本

>>> a = [1, 2, 3]

>>> b = a.copy()

>>> b[1] = 4

>>> a

[1, 2, 3]

count

>>> ['to', 'be', 'or', 'not', 'to', 'be'].count('to')

2

>>> x = [[1, 2], 1, 1, [2, 1, [1, 2]]]

>>> x.count(1)

2

>>> x.count([1, 2])

1

extend

>>> a = [1, 2, 3]

>>> b = [4, 5, 6]

>>> a.extend(b)

>>> a

[1, 2, 3, 4, 5, 6]

与加法的区别：

>>> a = [1, 2, 3]

>>> b = [4, 5, 6]

>>> a + b

[1, 2, 3, 4, 5, 6]

>>> a

[1, 2, 3]

如果要实现这个>>> a = a + b，加法的效率将比extend低

index

查找指定值第一次出现的索引

>>> knights = ['We', 'are', 'the', 'knights', 'who', 'say', 'ni']

>>> knights.index('who')

4

>>> knights.index('herring')

Traceback (innermost last):

File "<pyshell>", line 1, in ?

knights.index('herring')

ValueError: list.index(x): x not in list

找不到就报错

insert

>>> numbers = [1, 2, 3, 5, 6, 7]

>>> numbers.insert(3, 'four')

>>> numbers

[1, 2, 3, 'four', 5, 6, 7]

pop

>>> x = [1, 2, 3]

>>> x.pop()

3

>>> x

[1, 2]

>>> x.pop(0)

1

>>> x

[2]

返回弹出的值

与append相对

remove

删除第一个为指定值得元素

>>> x = ['to', 'be', 'or', 'not', 'to', 'be']

>>> x.remove('be')

>>> x

['to', 'or', 'not', 'to', 'be']

reverse

>>> x = [1, 2, 3]

>>> x.reverse()

>>> x

[3, 2, 1]

sort

就地排序

>>> x = [4, 6, 2, 1, 7, 9]

>>> x.sort()

>>> x

[1, 2, 4, 6, 7, 9]

>>> y = x.sort() # Don't do this!

>>> print(y)

None

另一个sorted不在原变量排序有返回值

>>> x = [4, 6, 2, 1, 7, 9]

>>> y = sorted(x)

>>> x

[4, 6, 2, 1, 7, 9]

>>> y

[1, 2, 4, 6, 7, 9]

>>> sorted('Python')

['P', 'h', 'n', 'o', 't', 'y']

sorted可用于任何序列（可迭代对象），但总返回一个列表

高级排序

这里有两个可选参数：key和reverse

>>> x = ['aardvark', 'abalone', 'acme', 'add', 'aerate']

>>> x.sort(key=len)

>>> x

['add', 'acme', 'aerate', 'abalone', 'aardvark']

>>> x = [4, 6, 2, 1, 7, 9]

>>> x.sort(reverse=True)

>>> x

[9, 7, 6, 4, 2, 1]

 

元组

与列表唯一差别在于元组不能修改

创建元组

>>> 1, 2, 3

(1, 2, 3) 

>>> (1, 2, 3)

(1, 2, 3)

空元组（列表也是这样）

>>> ()

()

加上逗号就是元组

>>> 42

42

>>> 42,

(42,)

>>> (42,)

(42,)

>>> 3 * (40 + 2)

126

>>> 3 * (40 + 2,)

(42, 42, 42)

tuple与list类似，将一个序列作为参数，转换为元组

>>> tuple([1, 2, 3])

(1, 2, 3)

>>> tuple('abc')

('a', 'b', 'c')

>>> tuple((1, 2, 3))

(1, 2, 3)

其它操作和列表差不多

>>> x = 1, 2, 3

>>> x[1]

2

>>> x[0:2]

(1, 2)