python_控制流

时间：2011-05-27 来源：邵国宝

1.if语句

#!/usr/bin/python
# Filename: if.py
number = 23
guess  = int(raw_input('Enter an integer:'))

if guess == number:
        print 'Congratulations, you guessed it' #New block starts here
        print '(but you do not win any prizes!)'#New block ends here
elif guess > number:
        print 'No, it is a little higher than that.'#Another block
else:
        print 'No, it is a little lower than that.'
print 'Done'
#This last statement is always executed, after the if statement is executed

python中没有switch语句，可以使用if..elif..else语句来完成同样的工作。

2.while语句

#!/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. '
                print 'but you do not win any prizes.'
                running = False #this cause the while loop to stop
        elif guess < number:
                print 'No, it is a little lower than that'
                print 'try again'
        else:
                print 'No, it is a little higher than that'
                print 'try again'
else:
        print 'The while loop is over.'
        #Do anything else you want to do here
print 'Done.'

python 中while可以和else连用

3.for循环

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

for i in range(1, 5):
    print i
else:
    print 'The for loop is over'

for i in range（1，5）相当于 for i in range [1,2,3,4]，即是在c/c++中的 for (int i = 0; i < 5; i++)。

同样，for也可以和else连用，else为可选部分

4.break语句

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

while True:
        s = raw_input('Enter something:')
        if s == 'quit':
                break;
        print 'Length of the string is', len(s)
print 'Done'

break跳出for或者while循环之后，不执行与while或者for配套的else（这个比较容易理解）

5.continue语句

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

while True:
        s = raw_input('Enter something:')
        if s == 'quit':
                break;
        print 'Length of the string is', len(s)
print 'Done'

continue对for语句同样适用

我们已经学习了如何使用三种控制流语句——if、while和for以及与它们相关的break和continue语句。它们是Python中最常用的部分，熟悉这些控制流是应当掌握的基本技能。

接下来，我们将学习如何创建和使用函数