Python中的while循环

while循环

while是python中执行循环的一个重要方法.只要条件是true,while语句会不断重复执行下去.
while循环的基本语法如下:
while test:
code statements
else:
final code statements

实例

x = 0

while x < 10:
    print('x is currently: ',x)
    print(' x is still less than 10, adding 1 to x')
    x+=1

执行结果:
x is currently: 0
x is still less than 10, adding 1 to x
x is currently: 1
x is still less than 10, adding 1 to x
x is currently: 2
x is still less than 10, adding 1 to x
x is currently: 3
x is still less than 10, adding 1 to x
x is currently: 4
x is still less than 10, adding 1 to x
x is currently: 5
x is still less than 10, adding 1 to x
x is currently: 6
x is still less than 10, adding 1 to x
x is currently: 7
x is still less than 10, adding 1 to x
x is currently: 8
x is still less than 10, adding 1 to x
x is currently: 9
x is still less than 10, adding 1 to x
请仔细看执行结果进行了多少次打印以及在条件x == 10满足前,while循环共进行了多少次.
我们在上面的代码基础上加上else

x = 0

while x < 10:
    print('x is currently: ',x)
    print(' x is still less than 10, adding 1 to x')
    x+=1
    
else:
    print('All Done!')

执行结果:
x is currently: 0
x is still less than 10, adding 1 to x
x is currently: 1
x is still less than 10, adding 1 to x
x is currently: 2
x is still less than 10, adding 1 to x
x is currently: 3
x is still less than 10, adding 1 to x
x is currently: 4
x is still less than 10, adding 1 to x
x is currently: 5
x is still less than 10, adding 1 to x
x is currently: 6
x is still less than 10, adding 1 to x
x is currently: 7
x is still less than 10, adding 1 to x
x is currently: 8
x is still less than 10, adding 1 to x
x is currently: 9
x is still less than 10, adding 1 to x
All Done!

break, continue, pass

如果我们的实际问题需要解决多种条件.可以在循环里使用break, continue, pass解决问题.
break指终止正在进行的最近的循环.
continue指回到最近的循环的开头.
pass指什么都不做.
加上break, continue,while循环的语法如下:

while test:
code statement
if test:
break
if test:
continue
else:
break和continue可以放在循环体里的任何位置,但是我们经常把它们放在嵌套if语句后面以在某种条件下执行操作.
实例

x = 0

while x < 10:
    print('x is currently: ',x)
    print(' x is still less than 10, adding 1 to x')
    x+=1
    if x==3:
        print('x==3')
    else:
        print('continuing...')
        continue

执行结果如下:
x is currently: 0
x is still less than 10, adding 1 to x
continuing...
x is currently: 1
x is still less than 10, adding 1 to x
continuing...
x is currently: 2
x is still less than 10, adding 1 to x
x==3
x is currently: 3
x is still less than 10, adding 1 to x
continuing...
x is currently: 4
x is still less than 10, adding 1 to x
continuing...
x is currently: 5
x is still less than 10, adding 1 to x
continuing...
x is currently: 6
x is still less than 10, adding 1 to x
continuing...
x is currently: 7
x is still less than 10, adding 1 to x
continuing...
x is currently: 8
x is still less than 10, adding 1 to x
continuing...
x is currently: 9
x is still less than 10, adding 1 to x
continuing...

x = 0

while x < 10:
    print('x is currently: ',x)
    print(' x is still less than 10, adding 1 to x')
    x+=1
    if x==3:
        print('Breaking because x==3')
        break
    else:
        print('continuing...')
        continue

输出结果:

x is currently: 0
x is still less than 10, adding 1 to x
continuing...
x is currently: 1
x is still less than 10, adding 1 to x
continuing...
x is currently: 2
x is still less than 10, adding 1 to x
Breaking because x==3