python 之生成器

斐波拉契数列：

In [31]: def func(times):
    ...:     alist = [0,1]
    ...:     sum = 0
    ...:     for i in range(times):
    ...:     
    ...:         sum  = alist[-2] + alist[-1]
    ...:         alist.append(sum)
    ...:         sum = 0
    ...:     return alist
    ...:  

In [32]: 

In [32]: print(func(5))
[0, 1, 1, 2, 3, 5, 8]

In [33]: print(func(10))
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

有趣的面试题：

在没有第三个数的情况下，实现两个数值交换，a = 10,b= 9,交换后a = 9 ,b = 10

In [34]: a = 10

In [35]: b = 9

In [36]: a = a + b

In [37]: b = a - b

In [38]: a = a - b

In [39]: a 
Out[39]: 9

In [40]: b
Out[40]: 10

################生成器######################

[root@master gaoji]# cat test.py
#!/usr/local/bin/python3
# -*- coding:utf-8 -*-

def creatNum():
    print('----start---')
    a,b = 0,1
    for i in range(5):
        print('---1---')
        yield b
        print('---2---')
        a,b = b,a + b
        print('---3---')
    print('----stop----')

结果：

In [1]: import test

In [2]: a = test.creatNum()

In [3]: next(a)
----start---
---1---
Out[3]: 1

In [4]: next(a)
---2---
---3---
---1---
Out[4]: 1

In [5]: next(a)
---2---
---3---
---1---
Out[5]: 2

In [6]: next(a)
---2---
---3---
---1---
Out[6]: 3

 

 ################生成器之传送数据send################

[root@master gaoji]# vim test1.py
  1 #!/usr/local/bin/python3
  2 # -*- coding:utf-8 -*-
  3 
  4 
  5 def test():         #第一次执行a.__next__() ,i=0,走到yield i,有yield返回数值0，此时停止不动，再执行a.__next__()，由yield 地方继续，此时并不是把yield i 的返回值
  6     i = 0            赋值给temp,此时temp的值为None,再继续i+=1,此时i=1，符合while条件，继续下面的语句，此时有yield i,返回yield 1的值，输出1，又停止不动，等待a.__next__()的调用执行，一直循环
  7     while i < 5:
  8         temp = yield i
  9         print(temp)
 10         i+=1

运行结果：

[root@master gaoji]# python3
Python 3.5.4 (default, Oct  7 2017, 12:39:20) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-17)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from test1 import *
>>> a = test()
>>> a
<generator object test at 0x7f35bca38258>
>>> a.__next__()
0
>>> a.__next__()
None
1
>>> a.__next__()
None
2

  >>> a.send("haha")    ###如果使用send,则是把值传给变量
  haha
  3
  >>> a.send("hello")
  hello
  4

 

 ###########使用案例场景##############

多任务案例，也就是多个任务同时进行