python生成器及yield关键字

简明示例：

1 def y():
2     for i in 'abc':
3         yield i

演示结果：

>>> x=y()
>>> next(x)
'a'
>>> next(x)
'b'
>>> next(x)
'c'
>>> next(x)
Traceback (most recent call last):
  File "<pyshell#6>", line 1, in <module>
    next(x)
StopIteration

 斐波那契数：

1 def fibonacciNum():
2     a,b=0,1
3     while True:
4         a,b=b,a+b
5         yield a

演示结果：

 1 >>> f=fibonacciNum()
 2 >>> next(f)
 3 1
 4 >>> next(f)
 5 1
 6 >>> next(f)
 7 2
 8 >>> next(f)
 9 3
10 >>> next(f)
11 5
12 >>> next(f)
13 8
14 >>> next(f)
15 13
16 >>> next(f)
17 21
18 >>> for i in f:
19     if i>50:
20         break
21     else:
22         print(i)
23 
24         
25 34
26 >>> for i in fibonacciNum():
27     if i>50:
28         break
29     else:
30         print(i)
31 
32         
33 1
34 1
35 2
36 3
37 5
38 8
39 13
40 21
41 34

 

 

自动生成可迭代序列：

 1 >>> a=[i for i in range(10)]　　#自动生成列表
 2 >>> a
 3 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
 4 >>> a=[i for i in range(10) if i%2]
 5 >>> a
 6 [1, 3, 5, 7, 9]
 7 >>> b={i:i+1 for i in range(10) if i%2}　　#自动生成字典
 8 >>> b
 9 {1: 2, 3: 4, 5: 6, 7: 8, 9: 10}
10 >>> c={i for i in (1,2,2,3,3,3,4,5,5)}　　#自动生成集合
11 >>> c
12 {1, 2, 3, 4, 5}
13 >>> s="i for i in 'abc'"　　#不可以自动生成字符串
14 >>> s
15 "i for i in 'abc'"
16 >>> t=(i for i in range(5))　　#不可以自动生成元组
17 >>> t
18 <generator object <genexpr> at 0x0000000003122360>　　#实际是生成器对象
19 >>> next(t)
20 0
21 >>> next(t)
22 1
23 >>> next(t)
24 2
25 >>> next(t)
26 3
27 >>> next(t)
28 4
29 >>> next(t)
30 Traceback (most recent call last):
31   File "<pyshell#43>", line 1, in <module>
32     next(t)
33 StopIteration
34 >>> for i in t:
35     print(i)
36 
37     #已经迭代到末尾，所以无值打印输出
38 >>> t=(i for i in range(5))
39 >>> for i in t:
40     print(i)
41 
42     
43 0
44 1
45 2
46 3
47 4
48 >>> sum(t)
49 0　　#已经迭代到末尾，所以求和为0
50 >>> t=(i for i in range(5))
51 >>> sum(t)
52 10

 

posted @ 2017-11-13 14:04  xiongjiawei  阅读(73)  评论(0)    收藏  举报