10.笨方法学python（习题30-33）

ゝ一世哀愁。 2023-03-13 05:28 45阅读 0赞

**习题30：Else和If**

people = 30 
         cars = 40 
         buses = 15 
         if people < cars: 
         print( "We should take the cars.") 
         elif people > cars: 
         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 should 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.")

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1.  猜想一下  elif 和  else 的功能。

> > elif后面可以接判断条件，为真执行其包含的语句；为假，跳过。
> 
> > else，在前面所有条件都为假的时候，执行。

2. 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。

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

people = 30 
         buses = 10 
         cars = 5 
         if people < (cars* 4): 
         print( "People can go by cars.") 
         elif people < (buses* 10): 
         print( "People can take buses.") 
         else: 
         print( "It's maybe hard for so many people go together.") 
         if people > cars and people > buses: 
         print( "Too many people.") 
         else: 
         print( "It's good!")

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4. 在每一行的上面写注解，说明这一行的功用。

**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( "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 = 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!")

习题32：循环和列表

要开始学列表了

the_count = [ 1, 2, 3, 4, 5] 
         fruits = [ 'apples', 'oranges', 'peers', 'apricots'] 
         change = [ 1, 'pennies', 2, 'dimes', 3, 'quarters'] 
         for number in the_count: 
         print( "This is count %d" % number) 
         for fruit in fruits: 
         print( "A fruit of type: %s" % fruit) 
         for i in change: 
         print( "I got %r" % i) 
         elements = [] 
         for i in range( 0, 6): 
         print( "Adding %d to the list." % i) 
         elements.append(i) 
         for i in elements: 
         print( "Element was: %d" % i)

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1.  注意一下  range 的用法。查一下 range 函数并理解它。

> range(start, stop\[, step\])
> 
> start默认为0；stop必填；step默认为1，必须为非零整数
> 
> range返回一个左闭右开\[left, right)的序列数
> 
>   
>

2. 在第 22 行，你可以可以直接将 elements 赋值为 range(0,6)，而无需使用 for 循环？

the_count = [ 1, 2, 3, 4, 5] 
         fruits = [ 'apples', 'oranges', 'peers', 'apricots'] 
         change = [ 1, 'pennies', 2, 'dimes', 3, 'quarters'] 
         for number in the_count: 
         print( "This is count %d" % number) 
         for fruit in fruits: 
         print( "A fruit of type: %s" % fruit) 
         for i in change: 
         print( "I got %r" % i) 
         elements = range( 0, 6) 
         for i in elements: 
         print( "Element was: %d" % i)

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3. 在 Python 文档中找到关于列表的内容，仔细阅读以下，除了  append 以外列表还支持哪些操作？

> Python基础教程——列表list：    [http://www.runoob.com/python/python-lists.html][http_www.runoob.com_python_python-lists.html]

习题33：while循环

i = 0 
         numbers = [] 
         while i < 6: 
         print( "At the top i is %d" % i) 
         numbers.append(i) 
         i = i + 1 
         print( "Number now:", numbers) # 注意逗号 
         print( "At the bottom i is %d" % i) 
         print( "-------------------------------") 
         print( "The numbers:") 
         for num in numbers: 
         print(num)

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1.  将这个 while 循环改成一个函数，将测试条件( i < 6 )中的  6 换成一个变量。

2. 使用这个函数重写你的脚本，并用不同的数字进行测试。

3. 为函数添加另外一个参数，这个参数用来定义第 8 行的加值  + 1 ，这样你就可以让它任意加值了。

4. 再使用该函数重写一遍这个脚本。看看效果如何。

i = 0 
         numbers = [] 
         n = int(input( ">")) #自行输入 
         while i < n: 
         print( "At the top i is %d" % i) 
         numbers.append(i) 
         i = i + 1 
         print( "Number now:", numbers) # 注意逗号 
         print( "At the bottom i is %d" % i) 
         print( "-------------------------------") 
         print( "The numbers:") 
         for num in numbers: 
         print(num)

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5. 接下来使用  for-loop 和  range 把这个脚本再写一遍。你还需要中间的加值操作吗？如果你不去掉它，会有什么样的结果？

不需要了。不去掉程序就不会停止。

numbers = [] 
         for i in range( 0, 6): 
         print( "At the top i is %d" % i) 
         numbers.append(i) 
         print( "Number now:", numbers) # 注意逗号 
         print( "At the bottom i is %d" % i) 
         print( "The numbers:") 
         for num in numbers: 
         print(num)

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很有可能你会碰到程序跑着停不下来了，这时你只要按着  CTRL 再敲  c (CTRL-c)，这样程序就会中断下来了。

今天差不多了，东西有点多。主要是**elif、if-else、for、range、while、list**

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[http_www.runoob.com_python_python-lists.html]: http://www.runoob.com/python/python-lists.html
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