python列表推导式

小鱼儿 2023-09-25 22:30 27阅读 0赞

python列表推导式创建列表的方式更简洁。常见的用法为，对序列或可迭代对象中的每个元素应用某种操作，用生成的结果创建新的列表；或用满足特定条件的元素创建子序列

plain_list = []   
    arguments="asdfghjkl"           
    for i in arguments:           
        for j in i:               
            plain_list.append(j)   
    
    print(plain_list)
    #['a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l']
    
    L1= list(arguments)
    print(L1)
    #['a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l']
    
    #squares = [x**2 for x in range(10)]
    squares = []
    for x in range(10):
        squares.append(x**2)
    print(squares)
    #[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
    
    str1 = list(map(lambda x: x**2, range(10)))
    print(str1)
    #[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
    
    #[(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]
    combs = []
    for x in [1,2,3]:
        for y in [3,1,4]:
            if x != y:
                combs.append((x, y))
    print(combs)
    #[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

\-嵌套的列表推导式  
列表推导式中的初始表达式可以是任何表达式，甚至可以是另一个列表推导式。  
下面这个 3x4 矩阵，由 3 个长度为 4 的列表组成：

>     matrix = [
>         [1, 2, 3, 4],
>         [5, 6, 7, 8],
>         [9, 10, 11, 12],
>     ]
>     print([[row[i] for row in matrix] for i in range(4)])
>     
>     transposed = []
>     for i in range(4):
>         transposed.append([row[i] for row in matrix])
>     print(transposed)
>     
>     transposed = []
>     for i in range(4):
>         # the following 3 lines implement the nested listcomp
>         transposed_row = []
>         for row in matrix:
>             transposed_row.append(row[i])
>         transposed.append(transposed_row)
>     print(transposed)
>     
>     #实际应用中，最好用内置函数替代复杂的流程语句。此时，zip() 函数更好用：
>     print(list(zip(*matrix)))
> 
> ![df0a1b1b0b2a487a881078ec2a16fe00.jpeg][]

[df0a1b1b0b2a487a881078ec2a16fe00.jpeg]: https://img-blog.csdnimg.cn/df0a1b1b0b2a487a881078ec2a16fe00.jpeg