習題 31: 作出決定

這本書的上半部分你打印了一些東西，而且調用了函數，不過一切都是直線式進行的。你的腳本從最上面一行開始，一路運行到結束，但其中并沒有決定程序流向的分支點。現在你已經學了 if, else, 和 elif ，你就可以開始創建包含條件判斷的腳本了。

上一個腳本中你寫了一系列的簡單提問測試。這節的腳本中，你將需要向用戶提問，依據用戶的答案來做出決定。把腳本寫下來，多多鼓搗一陣子，看看它的工作原理是什么。

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

door = raw_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 = raw_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 revolvers yelling melodies."

    insanity = raw_input("> ")
    
    if insanity == "1" or insanity == "2":
        print "Your body survives powered by a mind of jello.  Good job!"
    else:
        print "The insanity rots your eyes into a pool of muck.  Good job!"

else:
    print "You stumble around and fall on a knife and die.  Good job!"

這里的重點是你可以在“if 語句”內部再放一個“if 語句”。這是一個很強大的功能，可以用來創建嵌套(nested)的決定，其中的一個分支將引向另一個分支的子分支。

你需要理解 if 語句 包含 if 語句 的概念。做一下加分習題，這樣你會確信自己真正理解了它們。

你應該看到的結果

我在玩一個小冒險游戲，我玩的水平不怎么好：

$ python ex31.py 
You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 1
There's a giant bear here eating a cheese cake.  What do you do?
1. Take the cake.
2. Scream at the bear.
> 2
The bear eats your legs off.  Good job!

$ python ex31.py 
You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 1
There's a giant bear here eating a cheese cake.  What do you do?
1. Take the cake.
2. Scream at the bear.
> 1
The bear eats your face off.  Good job!

$ python ex31.py 
You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 2
You stare into the endless abyss at Cthuhlu's retina.
1. Blueberries.
2. Yellow jacket clothespins.
3. Understanding revolvers yelling melodies.
> 1
Your body survives powered by a mind of jello.  Good job!

$ python ex31.py 
You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 2
You stare into the endless abyss at Cthuhlu's retina.
1. Blueberries.
2. Yellow jacket clothespins.
3. Understanding revolvers yelling melodies.
> 3
The insanity rots your eyes into a pool of muck.  Good job!

$ python ex31.py 
You enter a dark room with two doors.  Do you go through door #1 or door #2?
> stuff
You stumble around and fall on a knife and die.  Good job!

$ python ex31.py 
You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 1
There's a giant bear here eating a cheese cake.  What do you do?
1. Take the cake.
2. Scream at the bear.
> apples
Well, doing apples is probably better.  Bear runs away.

加分習題

為游戲添加新的部分，改變玩家做決定的位置。盡自己的能力擴展這個游戲，不過別把游戲弄得太怪異了。