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 while loop 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 while loop 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 while loop 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 while loop to stop
    elif guess < number:
……

编写成

if guess == number:
        print 'Congratulations, you guessed it.'
         running = False # this causes the while loop to stop
    elif guess < number:
运行结果：

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

这一点不像其他语言那么灵活的。