习题 35: 分支和函数

你已经学会了 if 语句、函数、还有列表。现在你要练习扭转一下思维了。把下面的代码写下来，看你是否能弄懂它实现的是什么功能。

from sys import exit

def gold_room():
    print "This room is full of gold.  How much do you take?"

    next = raw_input("> ")
    if "0" in next or "1" in next:
        how_much = int(next)
    else:
        dead("Man, learn to type a number.")

    if how_much < 50:
        print "Nice, you're not greedy, you win!"
        exit(0)
    else:
        dead("You greedy bastard!")


def bear_room():
    print "There is a bear here."
    print "The bear has a bunch of honey."
    print "The fat bear is in front of another door."
    print "How are you going to move the bear?"
    bear_moved = False

    while True:
        next = raw_input("> ")

        if next == "take honey":
            dead("The bear looks at you then slaps your face off.")
        elif next == "taunt bear" and not bear_moved:
            print "The bear has moved from the door. You can go through it now."
            bear_moved = True
        elif next == "taunt bear" and bear_moved:
            dead("The bear gets pissed off and chews your leg off.")
        elif next == "open door" and bear_moved:
            gold_room()
        else:
            print "I got no idea what that means."


def cthulhu_room():
    print "Here you see the great evil Cthulhu."
    print "He, it, whatever stares at you and you go insane."
    print "Do you flee for your life or eat your head?"

    next = raw_input("> ")

    if "flee" in next:
        start()
    elif "head" in next:
        dead("Well that was tasty!")
    else:
        cthulhu_room()


def dead(why):
    print why, "Good job!"
    exit(0)

def start():
    print "You are in a dark room."
    print "There is a door to your right and left."
    print "Which one do you take?"

    next = raw_input("> ")

    if next == "left":
        bear_room()
    elif next == "right":
        cthulhu_room()
    else:
        dead("You stumble around the room until you starve.")


start()

你应该看到的结果

下面是我玩游戏的过程：

$ python ex35.py
You are in a dark room.
There is a door to your right and left.
Which one do you take?
> left
There is a bear here.
The bear has a bunch of honey.
The fat bear is in front of another door.
How are you going to move the bear?
> taunt bear
The bear has moved from the door. You can go through it now.
> open door
This room is full of gold.  How much do you take?
> asf
Man, learn to type a number. Good job!
$

加分习题

1. 把这个游戏的地图画出来，把自己的路线也画出来。
2. 改正你所有的错误，包括拼写错误。
3. 为你不懂的函数写注解。记得文档注解该怎么写吗？
4. 为游戏添加更多元素。通过怎样的方式可以简化并且扩展游戏的功能呢？
5. 这个 gold_room 游戏使用了奇怪的方式让你键入一个数字。这种方式会导致什么样的 bug？ 你可以用比检查 0、1 更好的方式判断输入是否是数字吗？int() 这个函数可以给你一些头绪。

常见问题回答

救命啊！太难了我搞不懂！

当你搞不懂的时候，就在*每一行*代码的上方写下注解，向自己解释这一行的功能。在这个过程中如果有了新的理解，就随时修正自己前面的注解。注解完后，就画一个工作原理的示意图，或者写一段文字表述一下。这样你就能弄懂了。

为什么是 while True:?

这样可以创建一个无限循环。

exit(0) 有什么功能？

在很多类型的操作系统里，``exit(0)`` 可以中断某个程序，而其中的数字参数则用来表示程序是否是碰到错误而中断。 exit(1) 表示发生了错误，而 exit(0) 则表示程序是正常退出的。这和我们学的布尔逻辑 0==False 正好相反，不过你可以用不一样的数字表示不同的错误结果。比如你可以用 exit(100) 来表示另一种和 exit(2)` 或 exit(1) 不同的错误。

为什么 raw_input() 有时写成 raw_input('> ')?

raw_input 的参数是一个会被打印出来的字符串，这个字符串一般用来提示用户输入。