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-8print "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:  60Hi, 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-8print "Please input your age: "age = int(raw_input())while age >= 60:    print "Hi, you shoudn\'t work !"    breakelse:    print "Sorry,Please continue work !"

执行结果：

[root@python ~]# python whitest.py Please input your age: 60Hi, you shoudn't work ![root@python ~]# python whitest.py Please input your age: 40Sorry,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-8print "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:  60Hi,you shoudn't work ![root@python ~]# python whitest1.py Please input your age:  40Sorry,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-8import randomprint "Please input number: ",num = int(raw_input())i = 0while 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-8import randomrandnum = random.randint(1,100)print "The random number is: %d " % randnumprint "Please input number: ",num = int(raw_input())i = 0while 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-8import randomrandnum = random.randint(1,100)print "The random number is: %d " % randnumwhile 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: 78Congratulations ! 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: 43Sorry ,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: 96Sorry,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: 543The input number should be in 1 to 100************random games****************Please input a interger number in 1 to 100: 12Sorry ,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-8num = 4while num:    if num % 4 == 0:        break        print "No exec !"     else:        print "%d is jishu" %num        num = 0print "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-8num = 9while 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。

完成于2017 05 12
凌晨00：24