Python学习之While循环

while循环

while循环是在高中学习过的知识，也就是高中所称的当型循环。意思就是当条件满足的时候，就执行循环体内的语句，如果不满足条件，则退出。

需求，如果年龄大于60，那么输出 hi,you shoudn’t work !,否则，输出，”please continue work !

方法一：使用if条件实现

#!/usr/bin/env python
#coding:utf-8

print "please input your age: ",
age = int(raw_input())

if age >= 60:
    print "hi, you shouldn\'t work !"
else:
    print "sorry,please continue work !"

执行结果：

[root@python ~]# python iftest1.py 
please input your age:  60
hi, you shouldn't work !
[root@python ~]# python iftest1.py 
please input your age:  40    
sorry,please continue work !

方法二：使用while循环
在使用while循环之前，有必要学习一下while循环的语法

while 循环语法
while condition:
statement

这是一个简单的while循环的语句，我们现在来看上面的需求该怎么实现。

#!/usr/bin/env python
#coding:utf-8

print "please input your age: "

age = int(raw_input())

while age >= 60:
    print "hi, you shoudn\'t work !"
    break
else:
    print "sorry,please continue work !"

执行结果：

[root@python ~]# python whitest.py 
please input your age: 
60
hi, you shoudn't work !
[root@python ~]# python whitest.py 
please input your age: 
40
sorry,please continue work !

上面就是一个while循环，但是，我们再里面增加了关键字break和else才能实现需求，但是我们也可以这么干。
在while当中使用if条件

#!/usr/bin/env python
#coding:utf-8

print "please input your age: ",

age = int(raw_input())

while true:
    if age >= 60:
        print "hi,you shoudn't work !"
        break
    else:
        print "sorry,please continue work !"
        break

执行结果：

[root@python ~]# python whitest1.py 
please input your age:  60
hi,you shoudn't work !
[root@python ~]# python whitest1.py 
please input your age:  40
sorry,please continue work !

但是，上面的方法并不怎么好，因为可读性不怎好！

关于while循环我也不知道该说些什么，反正就是提需求上代码 ！

玩一个小游戏：
需求，随机产生一个数和自己输入一个数做比较，如果输入的数字和随机的数字相等，那么提示“congratulations !the number is equal !”,如果输入的数字比随机产生的数字大 ，那么输出：”sorry, you age wrong,the number is more than random number !”,如果输入的数字比随机产生的数字小，那么输出：“sorry,you are wrong,the number is less than random number !”

话不多说，上代码 ：

#!/usr/bin/env python

#coding:utf-8
import random
print "please input number: ",
num = int(raw_input())
i = 0
while i <= 10:
    print "************random games****************"
    randnum = random.randint(1,100)
    x = 9 - i
    if num == randnum:
        print "congratulations ! the number %s is equal random %s" %(num,randnum)
        break
    elif num >= randnum:
        print "sorry ,you are wrong ,the number: %s is more than random: %s" %(num,randnum)
        break
    elif num <= randnum:
        print "sorry,you are wrong ,the number: %s is less than random: %s" %(num,randnum)
        break
    print "***********end games********************"
    i += 1

执行结果：

[root@python ~]# python game.py 
please input number:  10
************random games****************
sorry,you are wrong ,the number: 10 is less than random: 47
[root@python ~]# python game.py 
please input number:  53   
************random games****************
sorry ,you are wrong ,the number: 53 is more than random: 6
[root@python ~]# python game.py 
please input number:  76
************random games****************
sorry ,you are wrong ,the number: 76 is more than random: 62
[root@python ~]# 

发现这个游戏难度太大了，因为随机数是只有在条件为真的时候才产生的，所以，输入不知道多少次才能够成功，所以，现在来改一下代码，让随机数在在条件判断钱就产生，这样玩游戏就很明了。

#!/usr/bin/env python

#coding:utf-8
import random
randnum = random.randint(1,100)
print "the random number is: %d " % randnum
print "please input number: ",
num = int(raw_input())
i = 0
while i <= 10:
    print "************random games****************"
    x = 10 - i
    if num == randnum:
        print "congratulations ! the number %s is equal random %s" %(num,randnum)
        break
    elif num >= randnum:
        print "sorry ,you are wrong ,the number: %s is more than random: %s" %(num,randnum)
        break
    elif num <= randnum:
        print "sorry,you are wrong ,the number: %s is less than random: %s" %(num,randnum)
        break
    print "***********end games********************"
    i += 1

执行结果：

[root@python ~]# python game.py 
the random number is: 13 
please input number:  13
************random games****************
congratulations ! the number 13 is equal random 13
[root@python ~]# python game.py 
the random number is: 74 
please input number:  89
************random games****************
sorry ,you are wrong ,the number: 89 is more than random: 74
[root@python ~]# python game.py 
the random number is: 19 
please input number:  10
************random games****************
sorry,you are wrong ,the number: 10 is less than random: 19
[root@python ~]# 

这时候又有一个新的需求了，用户在任何时候输入数字的时候是不可靠的，那么就需要检测用户输入数字的有效性，如果用户输入的数字有效，那么用户输入的数字是否是在1–100之间呢？
我们需要对上述代码进行一个小小的修改。

#!/usr/bin/env python

#coding:utf-8
import random
randnum = random.randint(1,100)
print "the random number is: %d " % randnum
while true:
    print "************random games****************"
    num_input = raw_input("please input a interger number in 1 to 100: ")
    if not num_input.isdigit():
        print "please input a interger number: "
    elif int(num_input) < 0 or int(num_input) >= 100:
        print "the input number should be in 1 to 100"
    else:
        if randnum == int(num_input):
                print "congratulations ! the number %s is equal random %s" %(randnum,num_input)
                break
        elif randnum >= int(num_input):
                print "sorry ,you are wrong ,the number: %s is more than random: %s" %(randnum,num_input)
                break
        elif randnum <= int(num_input):
                print "sorry,you are wrong ,the number: %s is less than random: %s" %(randnum,num_input)
                break
        else:
                print "you should be a machine ! bye bye ."
~                                                                                                                      
~                                                               

说明:代码中对于判断是否为数字，使用num.isdigit( ) 函数
执行结果说明：

[root@python ~]# python game.py 
the random number is: 78 
************random games****************
please input a interger number in 1 to 100: 78
congratulations ! the number 78 is equal random 78
[root@python ~]# python game.py 
the random number is: 73 
************random games****************
please input a interger number in 1 to 100: 43
sorry ,you are wrong ,the number: 73 is more than random: 4
[root@python ~]# python game.py 
the random number is: 38 
************random games****************
please input a interger number in 1 to 100: 96
sorry,you are wrong ,the number: 38 is less than random: 96
[root@python ~]# python game.py 
the random number is: 95 
************random games****************
please input a interger number in 1 to 100: string      #输入一个字符串
please input a interger number: 
************random games****************
please input a interger number in 1 to 100: .           #输入一个半角句号
please input a interger number: 
************random games****************
please input a interger number in 1 to 100: /           #输入一个斜杠
please input a interger number: 
************random games****************
please input a interger number in 1 to 100: 343         #数字不在1到100之间
the input number should be in 1 to 100
************random games****************
please input a interger number in 1 to 100: 543
the input number should be in 1 to 100
************random games****************
please input a interger number in 1 to 100: 12
sorry ,you are wrong ,the number: 95 is more than random: 1
[root@python ~]# vi game.py 
[root@python ~]# 

while中的break和continue关键字

break和continue关键字经常出现杂循环当中，
break使用来当循环条件满足，执行语句块后马上跳出循环体，执行循环体外的语句。
continue则是从当前位置跳到循环体的最后一行的后面，但是不执行循环体内的最后一行，对于一个循环体来讲，最后一行的后面就是开始，继续执行一个循环体。
break

#!/usr/bin/env python

#coding:utf-8
num = 4
while num:
    if num % 4 == 0:
        break
        print "no exec !" 
    else:
        print "%d is jishu" %num
        num = 0

print "the number is %d " %num

执行结果：
[root@python ~]# python bretest.py
the number is 4
[root@python ~]#
说明break后面的print 语句并没有执行

continue

#!/usr/bin/env python

#coding:utf-8

num = 9
while num:
    if num % 4 == 0:
        num -= 1
        continue                                     #如果是偶数，就重新循环，直到条件为假
    else:
        print "the later number is %d " %num         #如果是奇数，那么输出奇数
        num -= 1

执行结果：
[root@python ~]# python contest.py
the later number is 9
the later number is 7
the later number is 6
the later number is 5
the later number is 3
the later number is 2
the later number is 1

while循环到这就结束了，接下来的学习就是要进行文件的学习了，文件的学习是非常重要的，尤其是那些喜欢学习网络爬虫的同学，文件的学习是必不可少的，因此，这一部分需要认真学习。明天更新，补昨晚没有更新的东西。