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列表推导式在逻辑上相当于一个循环,用[]进行包裹,常见的有如下三种方式

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方式一
    1个 for 循环

[Python] 纯文本查看 复制代码

In [1]: a = [x for x in range(4)]
In [2]: a
Out[2]: [0, 1, 2, 3]

    上述方法一相当于

[Python] 纯文本查看 复制代码

        In [12]: a = []
        In [13]: for x in range(4):
            ...:     a.append(x)
            ...:
        In [14]: a
        Out[14]: [0, 1, 2, 3]

方式二
    在循环过程中使用 if

[Python] 纯文本查看 复制代码

        In [102]: a = [ (x,y) for x in range(1,4) for y in range(3,6) if x != y ]
        In [103]: a
        Out[103]: [(1, 3), (1, 4), (1, 5), (2, 3), (2, 4), (2, 5), (3, 4), (3, 5)]

    上述方法二相当于

[Python] 纯文本查看 复制代码

        In [96]: n = []
        In [97]: for x in range(1,4):
            ...:     for y in range(3,6):
            ...:         if x != y:
            ...:             n.append((x,y))
        In [98]: n
        Out[98]: [(1, 3), (1, 4), (1, 5), (2, 3), (2, 4), (2, 5), (3, 4), (3, 5)]

方式三
    2个 for 循环

[Python] 纯文本查看 复制代码

        In [45]: a = [(x,y) for x in range(2) for y in range(3)]
        In [46]: a
        Out[46]: [(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2)]

    上述方法三相当于

[Python] 纯文本查看 复制代码

        In [53]: a = []
        In [54]: for x in range(2):
            ...:     for y in range(3):
            ...:         a.append((x,y))
        In [55]: a
        Out[55]: [(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2)]

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综上所述,列表推导式的形式如下:[ 表达式 for 变量 in 序列或迭代对象]

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扩展1
    根据上述方式一,我们可以扩展到以下的应用例子

[Python] 纯文本查看 复制代码

            In [21]: a = [' zhangsan',' lisi ','wangwu ']
            In [22]: a = [f.strip() for f in a]
            In [23]: a
            Out[23]: ['zhangsan', 'lisi', 'wangwu']

扩展2
    根据上述方式三,我们可以扩展到以下的应用例子

[Python] 纯文本查看 复制代码

            In [77]: a = [[1,2,3],[4,5,6],[7,8,9]]
            In [78]: [n for li in a for n in li]
            Out[78]: [1, 2, 3, 4, 5, 6, 7, 8, 9]

   该方法同理也相当于

[Python] 纯文本查看 复制代码

            In [71]: a = [[1,2,3],[4,5,6],[7,8,9]]
            In [72]: n = []
            In [73]: for li in a:
                ...:     for num in li:
                ...:         n.append(num)
            In [74]: n
            Out[74]: [1, 2, 3, 4, 5, 6, 7, 8, 9]

扩展3
    列表推导式支持文件对象迭代

[Python] 纯文本查看 复制代码

            In [114]: f = open('C:/Users/Administrator/Desktop/test.txt', 'r')
            In [115]: li = [line for line in f]
            In [116]: li
            Out[116]: ['python!']
            In [117]: f.close()

扩展4
    列表推导式快速生成九九乘法表

[Python] 纯文本查看 复制代码

            In [124]: print('\n'.join(['\t'.join('%d*%d=%d' % (y, x, x * y) for y in range(1, x + 1)) for x in range(1, 10)]))

            1*1=1
            1*2=2   2*2=4
            1*3=3   2*3=6   3*3=9
            1*4=4   2*4=8   3*4=12  4*4=16
            1*5=5   2*5=10  3*5=15  4*5=20  5*5=25
            1*6=6   2*6=12  3*6=18  4*6=24  5*6=30  6*6=36
            1*7=7   2*7=14  3*7=21  4*7=28  5*7=35  6*7=42  7*7=49
            1*8=8   2*8=16  3*8=24  4*8=32  5*8=40  6*8=48  7*8=56  8*8=64
            1*9=9   2*9=18  3*9=27  4*9=36  5*9=45  6*9=54  7*9=63  8*9=72  9*9=81

    该方法同理也相当于

[Python] 纯文本查看 复制代码

            In [123]: for x in range(1,10):
                ...:     for y in range(1,x+1):
                ...:         print('%d*%d=%d' % (y, x, x*y), end='\t')
                ...:     print(end='\n')

            1*1=1
            1*2=2   2*2=4
            1*3=3   2*3=6   3*3=9
            1*4=4   2*4=8   3*4=12  4*4=16
            1*5=5   2*5=10  3*5=15  4*5=20  5*5=25
            1*6=6   2*6=12  3*6=18  4*6=24  5*6=30  6*6=36
            1*7=7   2*7=14  3*7=21  4*7=28  5*7=35  6*7=42  7*7=49
            1*8=8   2*8=16  3*8=24  4*8=32  5*8=40  6*8=48  7*8=56  8*8=64
            1*9=9   2*9=18  3*9=27  4*9=36  5*9=45  6*9=54  7*9=63  8*9=72  9*9=81

奈斯