python学习之while语句

while语句在一个条件为真的情况下，

while

语句允许你重复执行一块语句。直接看例子：

#!/usr/bin/python
# Filename: while.py

number =

23

running =

True

while

running:

guess =

int

(

raw_input

(

'Enter an integer : '

))

if

guess == number:

print

'Congratulations, you guessed it.'

        running =

False

# this causes the whileloop to stop

elif

guess < number:

print

'No, it is a little higher than that'

else

:

print

'No, it is a little lower than that'

else

:

print

'The whileloop is over.' 

# Do anything else you want to do here

print

'Done'

当输入23时，程序执行done,结束，否则一直在循环（当然输入非整数时语法错误，程序会跳出的）。
运行结果：
$ python while.py
Enter an integer : 50
No, it is a little lower than that.
Enter an integer : 22
No, it is a little higher than that.
Enter an integer : 23
Congratulations, you guessed it.
The whileloop is over.
Done
//这里要说明的是python语言对空格要求的很严格，必须是对应的，否则语法是不正确的。例如上面例子中
……
if

guess == number:

print

'Congratulations, you guessed it.'

        running =

False

# this causes the whileloop to stop

elif

guess < number:

……
编写成
if

guess == number:

print

'Congratulations, you guessed it.'

         running =

False

# this causes the whileloop to stop

elif

guess < number:

运行结果：
File "while.py", line 12
running =False# this causes the whileloop to stop
^
SyntaxError: invalid syntax

这一点不像其他语言那么灵活的。