一行情书的浪漫之 九九乘法表

代码如下:

print('\n'.join('   '.join(['%s*%s=%-2s' % (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

---

写在前面:

1. join方法

• 用于将序列中的元素以指定的字符连接生成一个新的字符串。

str = '-';
seq = ('a','b','c');
print(str.join( seq ))
...
a-b-c

2. 列表生成式:

形如:

list = [x for x in range(5)]
print(list, type(list))
...
[0, 1, 2, 3, 4] <class 'list'>

3. 生成器:

生成器表达式与列表推导非常类似，使用列表推导 会一次产生所有结果。而使用生成器不会一次产生所有结果，它会返回按需产生结果的一个对象。如下所示：

obj = [x ** 2 for x in range(5)]
print(obj, type(obj))
...
[0, 1, 4, 9, 16] <class 'list'>

将列表推导的中括号换成圆括号，就是生成器表达式：

obj = (x ** 2 for x in range(5))
print(obj, type(obj))
...
<generator object <genexpr> at 0x7fe486d59eb8> <class 'generator'>

4. 一行情书 分解 伪代码 如下:

 obj3      =    ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]  

 obj2      =    '   '.join(        obj3        ) for x in range(1,10)   
 
 obj1      =    '\n'.join(       obj2      )     

print(  obj1  )            

---

解析: 层层 开扒:

1.

 obj3      =    ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]  

乘法表基本元素构造( x 相当于 九九乘法表 的第x行)
因为 for y in range(1,x+1)
所以需要根据 x 确定 y, 从而 确定 循环几次 继而 生成几个 列表元素

In [16]: x=1

In [17]: ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]
Out[17]: ['1 * 1 = 1 ']

In [18]: x=2

In [19]: ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]
Out[19]: ['1 * 2 = 2 ', '2 * 2 = 4 ']

In [20]: x=3

In [21]: ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]
Out[21]: ['1 * 3 = 3 ', '2 * 3 = 6 ', '3 * 3 = 9 ']

In [22]: x=9

In [23]: ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]
Out[23]:
['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']

2.

 obj2      =    '   '.join(        obj3        ) for x in range(1,10)   

for x in range(1,10)
循环遍历x等于(1...10); 每次都会提供给内部一个x;
' '.join( obj3 )
得到一个字符串

In [39]: x=1

In [40]: obj3 = ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]

In [41]:  '   '.join( obj3 )
Out[41]: '1 * 1 = 1 '

In [42]: x=2

In [43]:  '   '.join( obj3 )
Out[43]: '1 * 1 = 1 '

In [44]: obj3 = ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]

In [45]:  '   '.join( obj3 )
Out[45]: '1 * 2 = 2    2 * 2 = 4 '

In [46]: x=3

In [47]: obj3 = ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]

In [48]:  '   '.join( obj3 )
Out[48]: '1 * 3 = 3    2 * 3 = 6    3 * 3 = 9 '

In [49]: x=9

In [50]: obj3 = ['%s * %s = %-2s' % (y,x,x*y) for y in range(1,x+1)]

In [51]:  '   '.join( obj3 )
Out[51]: '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'

3.

 obj1      =    '\n'.join(       obj2      )                           

换行操作

4.

print(     obj1     )                                    

打印