Python生成器—— 斐波拉契数列

Posted 2020-10-09

斐波那契数列并不能用列表生产式表示，但能够用函数得出：

 1 #_*_coding:utf-8_*_
 2 #__author__ = "csy"
 3 def fib(max):
 4     n,a,b = 0,0,1
 5     while n < max:
 6         print(b)
 7         a,b = b,a + b  #初始a=0、b=1，a=b和b=a+b可理解为同时执行，即a=1、b=0+1=1
 8         n = n +1
 9     return ‘OK‘
10 
11 fib(9)

输出：

1
1
2
3
5
8
13
21
34

##################################华丽的分割线##########################################

将以上生成斐波拉契数列函数中的print (b)改为yield b则变成生成器

 1 #_*_coding:utf-8_*_
 2 #__author__ = "csy"
 3 def fib(max):
 4     n,a,b = 0,0,1
 5     while n < max:
 6         yield b
 7         a,b = b,a + b
 8         n = n + 1
 9     return ‘OK‘
10 
11 fib(9)

print(fib(9))输出：

<generator object fib at 0x00000000010E6A40>

##################################华丽的分割线##########################################

 1 f = fib(9)
 2 print(f.__next__())
 3 print(f.__next__())
 4 print(f.__next__())
 5 print(f.__next__())
 6 print(f.__next__())
 7 print(f.__next__())
 8 print(f.__next__())
 9 print(f.__next__())
10 print(f.__next__())
11 print(f.__next__())
12 print(f.__next__())
13 print(f.__next__())

使用next方法调用要注意调用次数，否则会出现报错 或 使用异常处理

1
1
2
3
5
8
13
21
34
Traceback (most recent call last):
File "C:/Users/chenshiyang/PycharmProjects/5.py", line 24, in <module>
print(f.__next__())
StopIteration: OK

##################################华丽的分割线##########################################

加入异常处理玩法：

 1 #_*_coding:utf-8_*_
 2 #__author__ = "csy"
 3 def fib(max):
 4     n,a,b = 0,0,1
 5     while n < max:
 6         yield b
 7         a,b = b,a + b
 8         n = n + 1
 9     return ‘Finish‘
10 
11 f = fib(9)
12 while True:
13     try:
14         x = next(f)
15         print(‘f:‘,x)
16     except StopIteration as e:
17         print(‘已经到头了‘, e.value)
18         break

输出：

f: 1
f: 1
f: 2
f: 3
f: 5
f: 8
f: 13
f: 21
f: 34
已经到头了 Finish