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.")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!")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)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)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
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)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)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)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
