Python08:列表

列表：python中以[]表示一个列表，取其中一个值是变量名[n]，n是代表列表中的下标值。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names)

输出：

['One', 'Two', 'Three', 'four']

Process finished with exit code 0

解释：

names = ["One","Two","Three","four"]：定义列表变量names，并设定names的值

print(names)：打印变量names

操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names[2])

输出：

Three

Process finished with exit code 0

解释：

print(names[2])：查询下标为2的元素（下标从0开始）。

切片操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names[1:2])

输出：

['Two']

Process finished with exit code 0

解释：

print(names[1:2])：切片操作，起始位置为1，终止位置为2，包含起始而不包含终止位置。

查询操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names[-1])

输出：

four

Process finished with exit code 0

解释：

print(names[-1])：查询最后一个元素。

切片操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names[-1:-3])

输出：

[]

Process finished with exit code 0

解释：

print(names[-1:-3])：错误的切片操作，起始位置要在终止位置的前边，故输出为空。

切片操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names[-3:-1])

输出：

['Two', 'Three']

Process finished with exit code 0

解释：

print(names[-3:-1])：同上一步比较，这个是正常的用负数作切片查询操作。

切片操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names[-2:])

输出：

['Three', 'four']

Process finished with exit code 0

解释：

print(names[-2:])：最后一位参数为空，则取到列表最后，此时包含最后一位元素。

切片操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names[0:3])
print(names[:3])

输出：

['One', 'Two', 'Three']

['One', 'Two', 'Three']

Process finished with exit code 0

解释：
print(names[:3])：如果起始索引不写，则从0开始查找，同print(names[0:3])一样的结果。

添加操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
names.append("LeiMing")
print(names)

输出：

['One', 'Two', 'Three', 'four', 'LeiMing']

Process finished with exit code 0

解释：

names.append("LeiMing")：向列表最后追加元素。

添加操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
names.insert(1,"Buck")
print(names)

输出：

['One', 'Buck', 'Two', 'Three', 'four']

Process finished with exit code 0

解释：

names.insert(1,"Buck")：向指定位置添加元素，第一个参数是下标位置，第二个参数是添加的值。

修改操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
names[2] = "Join"
print(names)

输出：

['One', 'Two', 'Join', 'four']

Process finished with exit code 0

解释：

names[2] = "Join"：元素的修改，找到修改的下标，直接赋值。

删除操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
names.remove("Three")
print(names)

输出：

['One', 'Two', 'four']

Process finished with exit code 0

解释：

names.remove("Three")：删除元素，参数填写要删除的值，直接删除。

删除操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
del names[1]
print(names)

输出：

['One', 'Three', 'four']

Process finished with exit code

解释：

del names[1]：删除下标为1的元素。

删除操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
names.pop()
print(names)

输出：

['One', 'Two', 'Three']

Process finished with exit code 0

解释：

names.pop()：删除操作，不写参数默认删除最后一位元素。

删除操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
names.pop(1)
print(names)

输出：

['One', 'Three', 'four']

Process finished with exit code 0

解释：

names.pop(1)：删除元素，填写数字，删除对应的下标的元素。

操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
print(names.index("Two"))

输出：

1

Process finished with exit code 0

解释：

print(names.index("Two"))：查询列表中元素是”Two”的下标。

方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four","Two","Two"]
print(names.count("Two"))

输出：

3

Process finished with exit code 0

解释：

print(names.count("Two"))：统计元素个数，此次统计为”Two”的元素个数。

方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","four"]
names.reverse()
print(names)

输出：

['four', 'Three', 'Two', 'One']

Process finished with exit code 0

解释：

names.reverse()：反转列表中的元素。

方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","2Two","#Three","four"]
names.sort()
print(names)

输出：

['#Three', '2Two', 'One', 'four']

Process finished with exit code 0

解释：

names.sort()：给列表中的元素排序，默认原则是以ASCII码的顺序，特殊字符、数字、大写字母、小写字母常见的。

方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","2Two","#Three","four"]
names.clear()
print(names)

输出：

[]

Process finished with exit code 0

解释：

names.clear()：清空列表。

方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","2Two","#Three","four"]
names2 = ["HanMei","LiLei","FengHua"]
names.extend(names2)
print(names)
print(names2)

输出：

['One', '2Two', '#Three', 'four', 'HanMei', 'LiLei', 'FengHua']

['HanMei', 'LiLei', 'FengHua']

Process finished with exit code 0

解释：

names.extend(names2)：将列表names2追加到names。

方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","2Two","#Three","four"]
names2 = ["HanMei","LiLei","FengHua"]
del names2
print(names)
print(names2)

输出：

['One', '2Two', '#Three', 'four']

Traceback (most recent call last):

  File "E:/python_code/s14/day2/names.py", line 10, in <module>

    print(names2)

NameError: name 'names2' is not defined

Process finished with exit code 1

解释：

del names2：删除names2，打印列表names2的时候报错，因为已删除。

浅拷贝方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","Four","Five"]
names2 = names.copy()

print(names)
print(names2)

输出：

['One', 'Two', 'Three', 'Four', 'Five']

['One', 'Two', 'Three', 'Four', 'Five']

Process finished with exit code 0

解释：

names2 = names.copy()：列表的拷贝，此方法是浅拷贝，何为浅拷贝，参考后边讲解。

浅拷贝方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","Four","Five",["JACK","ROSE"]]
names2 = names.copy()
names2[2] = "mclind"
names2[5][0] = "jack"

print(names)
print(names2)

输出：

['One', 'Two', 'Three', 'Four', 'Five', ['jack', 'ROSE']]

['One', 'Two', 'mclind', 'Four', 'Five', ['jack', 'ROSE']]

Process finished with exit code 0

解释：

可以看到，拷贝完列表，当改变names2当中的字符串时，只改变names2中的字符串，names当中的字符串不变，当改变names2列表当中的列表时，names当中的列表也跟着变化了。这是因为在浅复制当中，复制的是地址，并不是新创建了地址空间。字符串的是无法改变的（要想修改指向的字符串，变量名看起来不变，其实是新创建了一个字符串，变量名指向了新创建的字符串的地址，变量的值也就跟着变化了，而原来字符串的地址是不变的），所以names[2]指向的是字符串， 修改names[2]是指向了新的地址，而names没有修改，地址不变，值不受影响。当修改names[5][0]的时候，修改的是列表中列表，而列表中的列表的地址并没有改变，由于names[5]指向的地址没有改变，但names2修改了其中的内容，所以names指向的地址的内容也变化了，所以names2[5][0]的修改也影响了names的内容。

用指针更容易理解和解释，但python中并没有指针的概念。

浅拷贝还有别的方法：names2=copy.copy(names) 注：需导入copy模块。

                    names2=names[:]

                    names2=list(names)，三种结果一样，浅拷贝。

深复制方法操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind

import copy

names = ["One","Two","Three","Four","Five",["JACK","ROSE"]]
names2 = copy.deepcopy(names)
names2[2] = "mclind"
names2[5][0] = "jack"

print(names)
print(names2)

输出：

['One', 'Two', 'Three', 'Four', 'Five', ['JACK', 'ROSE']]

['One', 'Two', 'mclind', 'Four', 'Five', ['jack', 'ROSE']]

Process finished with exit code 0

解释：

names2 = copy.deepcopy(names)：导入copy模块，再使用深拷贝方法deepcopy()，深拷贝是完全独立的复制出来列表，开辟新的内存空间，一般不使用。

for循环的别样操作：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind


names = ["One","Two","Three","Four","Five",["JACK","ROSE"]]
for i in names:
    print(i)

输出：

One

Two

Three

Four

Five

['JACK', 'ROSE']

Process finished with exit code 0

解释：

遍历列表中的元素，然后打印出来。这时候也可以用步长切片。