笨方法学Python 习题 30: Else 和 If

#!usr/bin/python
# -*-coding:utf-8-*-

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 could 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.")

运行结果如下：

$ python ex30.py
We should take the cars.
Maybe we could take the buses.
Alright, let's just take the buses.
$

加分习题

猜想一下 elif 和 else 的功能。

将 cars, people, 和 buses 的数量改掉，然后追溯每一个 if 语句。看看最后会打印出什么来。

试着写一些复杂的布尔表达式，例如 cars > people and buses < cars。

在每一行的上面写注解，说明这一行的功用。

常见问题回答

如果多个 elif 区块都是 True 是 python 会如何处理?

Python 只会运行它碰到的是 True 的第一个区块，所以只有第一个为 True 的区块会被运行。