itertools模块:循环器

 

一,无穷循环器:count,cycle,repeat

(1)count(5,3)   #从5开始的整数循环器,每次增加3,即:5,8,11,14,17...

from itertools import *
import time
a = count(5,3)
for i in a:
    print(i)
    time.sleep(1)

输出结果为:
5
8
11
14
17
20
23
26
(2)cycle('zxy')  #重复元素x y z x y z x y z... 

from itertools import *
import time

s = cycle('xyz')

for i in s:
    print(i)
    time.sleep(1)

输出结果为:
x
y
z
x
y
z
x
y
z
repeat()   #重复元素

例1:
from itertools import *
import time

s = repeat(3.14)  #无限重复元素

for i in s:
    print(i)
    time.sleep(1)

输出结果为:
3.14
3.14
3.14
3.14
3.14
3.14

例2:
from itertools import *
import time

s = repeat(3,5)   #重复元素3,共5次

for i in s:
    print(i)
    time.sleep(1)

输出结果为:
3
3
3
3
3

 

二,函数式工具:starmap,takewhile,dropwhile

(1)starmap()    #跟map类似

from itertools import *

s = starmap(pow,[(1,1),(2,2),(3,3)])  #pow()求指数1**1,2**2,3**3
for i in s:
    print(i)

输出结果为:
1
4
272)takewhile()   #当函数返回True时,收集元素到循环器。一旦函数返回False,则停止。

from itertools import *

s1 = takewhile(lambda x: x < 5, [1,2,3,4,5,6,7])
for i in s1:
    print(i)

输出结果为:
1
2
3
43)dropwhile()   #与takewhile相反。

s2 = dropwhile(lambda x: x < 5, [1,2,3,4,5,6,7])
for i in s2:
    print(i)

输出结果为:
5
6
7

 

posted on 2016-12-21 17:45  PingY  阅读(323)  评论(0编辑  收藏  举报