《 笨方法学 Python 》_ 习题 27 - 31

习题 27：记住逻辑关系

    逻辑术语

        and         与
        or          或
        not         非
        !=          不等于
        ==          等于
        >=          大于等于
        <=          小于等于
        True        真
        False       假

习题 28：布尔表达式练习

习题 29：if 语句

people = 20
cats = 30
dogs = 15

if people < cats:
    print("Too many cats! The world is doomed!")
    
if people > cats:
    print("Not many cats! The world is saved!")
    
if people < dogs:
    print("The world is drooled on!")
    
if people > dogs:
    print("The world is dry!")
    
dogs += 5

if people >= dogs:
    print("People are greater than or equal to dogs.")
    
if people <=dogs:
    print("People are less than or equal to dogs.")
    
if people == dogs:
    print("People are euqal to dogs.")

习题 30：else 和 if

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.")

常见问题回答：

如果多个 elif 块都是 True，Python 会如何处理？

Python 只会运行它遇到的是 True 的第一个块，所以只有第一个为 True 的块会运行。

习题 31：做出决定

print("You enter a dark room with two doors. Do you go through door #1 or door #2?")

door = input("> ")

if door == "1":
    print("There's a giant bear here eating a cheese cake. What do you do?")
    print("1. Take the cake.")
    print("2. Scream at the bear.")
    
    bear = input("> ")
    
    if bear == "1":
        print("The bear eats your face off. Good job!")
    elif bear == "2":
        print("The bear eats your legs off. Good job!")
    else:
        print("Well, doing %s is probably better. Bear runs away." % bear)
        
elif door == "2":
    print("You stare into the endless abyss at Cthulhu's retina.")
    print("1. Blueberries.")
    print("2. Yellow jacket clothespins.")
    print("3. Understanding rebolvers yelling melodies.")
    
    insanity = input("> ")
    
    if insanity == "1" or insanity == "2":
        print("Your body survives powered by a mind of jelllo. Good job!")
    else:
        print("The insanity rots your eyes into a pool of muck. Good job!")
        
else:
    print("Your stumble around and fall on a knife and die. Good job!")