EX30

people = 30
cars = 40
buses = 15

if cars > people:
    print "We should take the cars."
elif cars < people:
    print "We should not take the cars."
else:
    print "We can't decide."

if buses > cars:
    print "That's too many buses."
elif buses < cars:
    print "Maybe we chould take the buses."
else:
    print "We still can't decide."
    
if people > buses:
    print "Alright, let's just take the buses."
else:
    print "Fine, let's stay home then."

 

Study Drills

1、Try to guess what elif and else are doing.

　　elif & else 是子句，因为它们不能独立使用，两者都是出现在if、for、while语句内部的。else子句可以增加一种选择；而elif子句则是需要检查更多条件时会被使用，与if和else一同使用，elif是else if 的简写。

num = 0
if num > 0 :
    print '这个数比0大'
elif num < 0 :
    print '这个数比0小'
else :
    print '这个数是0'

程序分别对if和elif做了判断，如果条件不为真，则输出else的语句块内容。程序运行结果是：这个数是0

需留意：

　　1、else、elif为子块，不能独立使用
　　2、一个if语句中可以包含多个elif语句，但结尾只能有一个else语句