Python 学习笔记8 循环语句 while

While循环是哟中利用条件语句，不断的执行某一段代码块，达到批量操作输出等一系列的操作，直到条件不满足或者被强制退出为止。

其工作流程如下：（图片来源菜鸟教程：http://www.runoob.com/python/python-while-loop.html ）

我们来看一个例子：

current_number = 10

while current_number <= 20:

    print("Current number is : " + str(current_number))

    current_number += 1

print("Final number: " + str(current_number))

'''

输出：

Current number is : 10

Current number is : 11

Current number is : 12

Current number is : 13

Current number is : 14

Current number is : 15

Current number is : 16

Current number is : 17

Current number is : 18

Current number is : 19

Current number is : 20

Final number: 21

'''

我们可以看到变量current_number 的初始值为10，在小于等于20的情况下，不断的被打印，被增长，直至增长到21的时候，跳出了循环。

我们也可以使用标志，比如True,False 等布尔值来进行循环：

flag = True

while flag:

    number = int(input("Input a number less than 10:\n"))

    if number < 10:

        flag = True

    else:

        flag = False

print("The game is end...")

'''

输出：

Input a number less than 10:

2

Input a number less than 10:

11

The game is end...

Final number: 21

'''

使用 break 退出循环。在while循环中，你可以通过特定的条件语句，选择终止循环，不再继续运行余下的代码。

flag = True

while flag:

    city = input("Input a city which you like: \n" + "Input 'Q' to quit...\n")

    if city == 'Q':

        break

    else:

        print("You like " + city)

print("Thanks for your information.")

'''

输出：

Input a city which you like:

Input 'Q' to quit...

ShangHai

You like ShangHai

Input a city which you like:

Input 'Q' to quit...

HangZhou

You like HangZhou

Input a city which you like:

Input 'Q' to quit...

Q

Thanks for your information.

'''

使用 continue 不再继续执行余下的代码块，返回到循环开头，继续下一轮循环。

number = 0

while number <= 10:

    if number % 2 == 0:

        print("The number is even: " + str(number))

        number += 1

        continue

        print("Next...")

    else:

        number += 1

'''

输出：

The number is even: 0

The number is even: 2

The number is even: 4

The number is even: 6

The number is even: 8

The number is even: 10

'''

循环也可以和else 一起使用：

number = 0

while number <= 10:

    if number % 2 == 0:

        print("The number is even: " + str(number))

        number += 1

        continue

        print("Next...")

    else:

        number += 1

else:

    print("The number is equal or more than 10, stop loop.")

'''

输出：

The number is even: 0

The number is even: 2

The number is even: 4

The number is even: 6

The number is even: 8

The number is even: 10

The number is equal or more than 10, stop loop.

'''

使用while 操作列表 List

peoples = ['Ralf', 'Clark', 'Leon']

while peoples:

    people = peoples.pop()

    print(people)

'''

输出：

Leon

Clark

Ralf

'''

peoples = ['Ralf', 'Clark', 'Leon', 'Terry']

while 'Terry' in peoples:

    peoples.remove('Terry')

    print(peoples)

'''

输出：

['Ralf', 'Clark', 'Leon']

'''

while循环语句可以解决程序中需要重复执行的操作。其循环执行的次数由循环条件确定，当循环条件满足时，重复执行某程序段，直到循环条件不成立为止。反复执行的程序段称为循环体，循环条件必须要在循环体中改变，否则可能会出现无限循环的结果

巴特西

Python 学习笔记8 循环语句 while

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