习题31：作出决定

代码

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.")
    print("What do you da?")
    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("The bear eats your legs off.Good job!")
    else:
        print(f"Well,doing {bear} is probably better.")
        print("Bear runs away.")

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 revolver yelling melogies.")

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

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

PS C:\Users\WU\pyfile> 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 da?
1.Take the cake.
2.Scream at the bear.
>2
The bear eats your legs off.Good job!

横竖都得死。。。

知识点

• 使用1<x<10 或 1<= x <10 ,或者x in range (1,10)这种经典语法去判定一个数是否处于某个值域。
• if-elif-else 还可以继续增加为 if-elif-elif-elif-else 等等。
• if语句内部还有一个if语句作为可运行的代码，这种嵌套的手法把一个分支引向另一个分支的子分支。
• elif必须和if一起使用，否则出错。else 一般用在最后，即所有条件都不满足时使用。
• if-else组合是可以替代elif的。不过python只有遇到第一个True就停下当前判断。这篇if-else-elif-if嵌套比较清晰一些。

---

习题32：循环和列表

代码

the_count = [1,2,3,4,5]
fruits = ['apple','oranges','pears','apricots']
change= [1,'pennies',2,'dimes',3,'quarters']

#this first kind of for-loop goes through a list
for number in the_count:
    print(f"This is count {number}")

# same as above
for fruit in fruits:
    print(f"A fruit if type : {fruit}")

#also we can go through mixed lists too
#notice we have to use {} since we don't know what's in it

for i in change:
    print(f"I got {i}")

# we can also build lists,first start with an empty one
elements  = []

#then use the range  function to do 0 to 5 coounts
for i in range(0,6):
    print(f"Adding {i} to the list.")
    #append is a function that lists understand
    elements.append(i)

#now we can print them out too
for i in elements:
    print(f"Element was :{i}")

PS C:\Users\WU> cd pyfile
PS C:\Users\WU\pyfile> python ex32.py
This is count 1
This is count 2
This is count 3
This is count 4
This is count 5
A fruit if type : apple
A fruit if type : oranges
A fruit if type : pears
A fruit if type : apricots
I got 1
I got pennies
I got 2
I got dimes
I got 3
I got quarters
Adding 0 to the list.
Adding 1 to the list.
Adding 2 to the list.
Adding 3 to the list.
Adding 4 to the list.
Adding 5 to the list.
Element was :0
Element was :1
Element was :2
Element was :3
Element was :4
Element was :5

知识点

• 列表（list）创建方式： list = [a,b,c,d,e,f] 左方括号 “[” 表示“打开”列表，逗号隔开元素，右边括号 “]” 表明列表结束。
• range的功能：回一个递进的整数的列表。range的用法：range（起始位，结束位，步数）,注意range的起始位和结束位构成的区间是一个前闭后开的，即range()函数会从第一个数到最后一个数，但不包含最后一个数字。例如range（0,10,2）是[0，2,4,6,8] .
• [[0,1,2],[0,1,2]] 这是二维列表，即列表中包含列表。
• for value in variable: 中value变量在for循环开始就已经被创立，每次循环value都会被重新初始化为当前循环中的 元素值。

函数	作用
cmp(list1, list2)	比较两个列表的元素
len(list)	列表元素个数
max(list)	返回列表元素最大值
min(list)	返回列表元素最小值
list(seq)	将元组转换为列表
list.append(obj)	在列表末尾添加新的对象
list.count(obj)	统计某个元素在列表中出现的次数
list.extend(seq)	在列表末尾一次性追加另一个序列中的多个值（用新列表扩展原来的列表）
list.index(obj)	从列表中找出某个值第一个匹配项的索引位置
list.insert(index, obj)	将对象插入列表
list.pop([index=-1])	移除列表中的一个元素（默认最后一个元素），并且返回该元素的值
list.remove(obj)	移除列表中某个值的第一个匹配项
list.reverse()	反向列表中元素
list.sort(cmp=None, key=None, reverse=False)	对原列表进行排序

---

习题33：while循环

代码

from typing import Sequence
i = 0
numbers = []

Seq = 5
while i < 6:
    print(f"At the top i is {i}")
    numbers.append(i)
    i += Seq
    print(f"At the bottom i is {i}")
print("The numbers:")

for num in numbers:
    print(num)

PS C:\Users\WU\pyfile> python ex33.py
At the top i is 0
At the bottom i is 1
At the top i is 1
At the bottom i is 2
At the top i is 2
At the bottom i is 3
At the top i is 3
At the bottom i is 4
At the top i is 4
At the bottom i is 5
At the top i is 5
At the bottom i is 6
The numbers:
0
1
2
3
4
5

def app(steps,max):
    numbers = []
    i  = 0
    while i < max:
        numbers.append(i)
        i += steps
        print(numbers)
app(2,10)

PS C:\Users\WU> & python c:/Users/WU/pyfile/py33test.py
[0]
[0, 2]
[0, 2, 4]
[0, 2, 4, 6]
[0, 2, 4, 6, 8]

知识点

• ctrl C 终止循环
• while循环有时候会永远无法停止。注意尽量少用while 循环，大部分时候for 循环 是更好的选择。重复检查你的while语句，确定测试的布尔表达式最终会变成False。如果不确定，就在while 循环的开始和结尾打印出你要测试的值，看看它的变化
• for循环只能对一些东西的集合进行循环，while 循环可以对任何对象进行循环。然而，相比起来while 循环更难弄对，而对一般任务用 for 循环更容易一些。
• while语义很简单，但条件判断为True 时，循环重复执行语句块中的语句；当条件为False时，循环终止，执行与while同级别缩进的后续语句。
• while 还可以和else结合

while <语句>：
    <语句块1>
else：
    <语句块2>

---

习题34：访问列表的元素

代码

animals = ["bear",'python',"peacock","kangeroo","whale","platypous"]
print("位置1:"+animals[1])
print("第3只:"+animals[2])
print("第一只:"+animals[0])
print("位置3:"+animals[3])
print("第5只:"+animals[4])
print("位置3:"+animals[3])
print("第6只:"+animals[5])
print("位置4:"+animals[4])

PS C:\Users\WU> & python c:/Users/WU/pyfile/ex34.py
位置1:python
第3只:peacock
第一只:bear
位置3:kangeroo
第5只:whale
位置3:kangeroo
第6只:platypous
位置4:whale

知识点

• 简单地说序数从1开始，基数从0开始，序数符合人类的思维，基数符合计算机的思维。序数（ordinal number）：从1开始编号，表示事物的顺序
• 基数（cardinal number）：从0开始，表示你可以任意抓取元素
• 序数（ordinal number）：从1开始编号，表示事物的顺序

---

习题35：分支和函数

代码

from sys import exit
from typing import DefaultDict

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

    choice = input(">")

    if "0" in choice or "1" in choice:
        how_much = int(choice)
    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:
        choice = input("> ")

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

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

    choice = input("> ")

    if "flee" in choice:
        start()
    elif "head" in choice:
        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?")

    choice = input("> ")

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

start()

PS C:\Users\WU\pyfile> 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 the door
I got no idea what that means.
> open door
This room is full of gold. How much do you take?
>25
Man,learn to type a number. Good job!

知识点

·

• while True表示一个无限循环。
• exit(0) 可以终止某个程序，而其中的数字参数则用来表示是否遇到错误而终止。exit(1) （或大于 1）表示程序执行失败发生错误并退出程序，而exit(0) 则表示程序是正常退出的。
• input(“> ”)里面的>是用来提示用户输入的，比较人机交互吧。