Python文本游戏：使用while循环和try-except的猜数字游戏

Question

我正在写一个简单的文字游戏，目的是提高我对Python的理解。在游戏的一个阶段，用户需要在1到5之间猜一个数字，才能实现他们的愿望。他们只有三次机会。我有两个问题：

1) 假设genie_number随机选定为3。这个值在用户每次猜测后会改变吗？我不想让程序在每次猜测后随机选择另一个数字。它应该保持不变，这样用户就有3/5的机会猜对。

2) 我想惩罚那些没有猜整数的用户，我在except ValueError部分做了这个。但如果用户连续三次猜非整数并用完所有机会，我希望循环能跳转到else: dead("精灵把你变成了一只青蛙。")。现在它给我下面的错误信息。我该怎么解决这个问题？

'Before I grant your first wish,' says the genie, 'you must answer this
'I am thinking of a discrete integer contained in the set [1, 5]. You ha
(That isn't much of a riddle, but you'd better do what he says.)
What is your guess? > what
That is not an option. Tries remaining: 2
What is your guess? > what
That is not an option. Tries remaining: 1
What is your guess? > what
That is not an option. Tries remaining: 0
Traceback (most recent call last):
  File "ex36.py", line 76, in <module>
    start()
  File "ex36.py", line 68, in start
    lamp()
  File "ex36.py", line 48, in lamp
    rub()
  File "ex36.py", line 38, in rub
    wish_1_riddle()
  File "ex36.py", line 30, in wish_1_riddle
    if guess == genie_number:
UnboundLocalError: local variable 'guess' referenced before assignment

这是我目前的代码：

def wish_1_riddle():
    print "\n'Before I grant your first wish,' says the genie, 'you must answer this riddle!'"
    print "'I am thinking of a discrete integer contained in the set [1, 5]. You have three tries.'"
    print "(That isn't much of a riddle, but you'd better do what he says.)"

    genie_number = randint(1, 5)
    tries = 0
    tries_remaining = 3

    while tries < 3:
        try:
            guess = int(raw_input("What is your guess? > "))
            tries += 1
            tries_remaining -= 1

            if guess == genie_number:
                print "Correct!"
                wish_1_grant()
            else:
                print "Incorrect! Tries remaining: %d" % tries_remaining
                continue
        except ValueError:
            tries += 1
            tries_remaining -= 1
            print "That is not an option. The genie penalizes you a try. Be careful!"
            print "Tries remaining: %d" % tries_remaining

    if guess == genie_number:
        wish_1_grant()
    else:
        dead("The genie turns you into a frog.")

Answer 1

回答你的第一个问题，不会。如果你一直调用 randint(1, 5)，结果会变化，但一旦你把这个随机数赋值给某个变量，它的值就固定了：

>>> import random
>>> x = random.randint(1, 10)
>>> x
8
>>> x
8
>>> x
8
>>> random.randint(1, 10)
4
>>> random.randint(1, 10)
8
>>> random.randint(1, 10)
10

正如你所看到的，一旦我们把随机数赋值给 x，x 就一直保持不变。不过，如果我们继续调用 randint()，结果就会变化。

回答你的第二个问题，你不应该在 int(raw_input()) 后面直接给 tries 加 1，如果这个值是整数，它也会给 tries 加 1。相反，试着把你的代码整合成下面这样的形式：

>>> tries = 0
>>> while tries < 3:
...     try:
...             x = raw_input('Hello: ')
...             x = int(x)
...     except ValueError:
...             tries+=1
... 
Hello: hello
Hello: 1
Hello: 4
Hello: bye
Hello: cool
>>> 

你遇到错误是因为你三次都回答错了。因此，guess 没有被赋值。在你的 while 循环后，你试图检查 guess 是否有值，但实际上它没有：

>>> tries = 0
>>> while tries < 3:
...     try:
...             guess = int(raw_input('Enter input: '))
...             print guess
...     except ValueError:
...             tries+=1
... 
Enter input: hello
Enter input: bye
Enter input: good morning
>>> guess
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'guess' is not defined

不过，如果你输入正确，guess 就会有值：

>>> tries = 0
>>> while tries < 3:
...     try:
...             guess = int(raw_input('Enter input: '))
...             print guess
...     except ValueError:
...             tries+=1
... 
Enter input: 4
4
Enter input: hello
Enter input: 9
9
Enter input: bye
Enter input: 6
6
Enter input: greetings
>>> guess
6
>>> 

编辑

与 @LosFrijoles

>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> for k in range(1):
...     x = 1
...     print x
... 
1
>>> x
1
>>> 

正如你所看到的，变量 x 在 for 循环和普通的环境中都存在，所以这不是作用域问题：

>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> for k in range(1, 3):
...     try:
...             x = int(raw_input('Hello: '))
...             print x 
...     except ValueError:
...             pass
... 
Hello: hello
Hello: bye
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> 

如你所见，这确实是个错误... :) 由于这个错误，x 永远不会被赋值，除非我们实际输入一个整数，因为代码从未到达 print x，因为它因为错误而中断：

>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> for k in range(1, 3):
...     try:
...             x = int(raw_input('Hello: '))
...             print x
...     except ValueError:
...             pass
... 
Hello: hello
Hello: 8
8
>>> x
8
>>> 

当我们确实输入一个整数时，x 就变得有效了。