《笨方法学Python》加分题 40

习题 40：模块、类和对象

字典和模块使用方式有点类似，只是语法不同（[键]和.键）：

Python里一个通用模式：1）类似“键=值”风格的容器；2）通过“键”的名称获取其中的值

模块是包含函数和变量的 Python 文件，可以导入这个文件，可以使用 "." 操作符访问模块中的函数和变量。

模块还可以用一种方法去理解：可以把它们当做一种特殊的字典，通过它们可以存储一些 Python 代码，可以通过 "." 操作符访问这些代码。Python 还有一种另外一种代码结构用来实现类似的目的，那就是类，通过类，你可以把一组函数和数据放到一个容器中，从而用 "." 操作符访问类中的函数和变量。

使用类而非模块的原因：其重复创建很多出来（类可以多次实例化），这些实例之间也不会相互干涉；而模块一次导入之后，整个程序中只有这么一份内容

对象相当于迷你导入

 

现在有三种方法可以从某个东西里获取东西：

# dict sytle
mystuff['apples']
 
# module style            调用模块
mystuff.apples()        # 访问模块的函数
mystuff.tangerine       # 访问模块的变量
 
# class style
thing = MyStuff()         调用类
thing.apples()          # 访问类的函数
thing.tangerine         # 访问类的变量

class Song:
    
    def __init__(self, lyrics):
        self.lyrics = lyrics
        
    def sing_me_a_song(self):
        for line in self.lyrics:
            print(line)
            
happy_bday = Song(["Happy birthday to you",            # 调用类
                   "I don't want to get sued",
                   "So I'll stop right there"])
 
bulls_on_parade = Song(["There rally around the family",
                        "With pockets full of shells"])
                        
happy_bday.sing_me_a_song()
 
bulls_on_parade.sing_me_a_song()

创建 __init__ 或者别的类函数时需要多加一个 self 变量。

习题 41：学习面向对象术语

import random
from urllib.request import urlopen
import sys

WORD_URL = "http://learncodethehardway.org/words.txt"
WORDS = []

PHRASES = {
    "class %%%(%%%):":
      "Make a class named %%% that is-a %%%.",
    "class %%%(object):
	def __init__(self, ***)" :
      "class %%% has-a __init__ that takes self and *** params.",
    "class %%%(object):
	def ***(self, @@@)" :    
      "class %%% has-a function *** that takes self and @@@ params.",
    "*** = %%%()":
      "Set *** to an instance of class %%%.",
    "***.***(@@@)":
      "From *** get the *** function, call it with params self, @@@.",
    "***.*** = '***'":
      "From *** get the *** attribute and set it to '***'."
}

# do they want to drill phrases first
if len(sys.argv) == 2 and sys.argv[1] == "english":
    PHRASE_FIRST = True
else:
    PHRASE_FIRST = False

# load up the words from the website
for word in urlopen(WORD_URL).readlines():
    WORDS.append(str(word.strip(), encoding = "utf-8"))

def convert(snippet, phrase):
    class_names = [w.capitalize() for w in
                   random.sample(WORDS, snippet.count("%%%"))]
    other_names = random.sample(WORDS, snippet.count("%%%"))  
    results = []
    param_names = []

    for i in range(0, snippet.count("@@@")):
        param_count = random.randint(1,3)
        param_names.append(','.join(
            random.sample(WORDS, param_count)))

    for sentence in snippet, phrase:
        result = sentence[:]

        #fake class names
        for word in class_names:
            result = result.replace("%%%", word, 1)
        #fake other names
        for word in other_names:
            result = result.replace("***", word, 1)
        #fake parameter names
        for word in param_names:
            result = result.replace("@@@", word, 1)

        results.append(result)
    return results

# keep going until they hit CTRL-D
try:
    while True:
        snippets = list(PHRASES.keys())
        random.shuffle(snippets)

        for snippet in snippets:
            phrase = PHRASES[snippet]
            question, answer = convert(snippet, phrase)
            if PHRASE_FIRST:
                question, answer = answer, question

            print(question)

            input("> ")
            print(f"ANSWER: {answer}

")

except EOFError:
    print("
Bye")

    result = sentence[:]
    print(result)

习题 42：对象、类及从属关系

## Animal is-a object (yes, sort of confusing) look at the extra credit
class Animal(object):
    pass

## Dog is-a Animal
class Dog(Animal):

    def __init__(self, name):
        ## ??
        self.name = name

## Cat is-a Animal
class Cat(Animal):

    def __init__(self, name):
        ## ??
        self.name = name
    
## Person is-a Animal
class Person(Animal):

    def __init__(self, name):
        ## ??
        self.name = name
        
        ## Person has-a pet of some kind
        self.pet = None

## Employee is-a Person
class Employee(Person):

    def __init__(self, name, salary):
        ## ?? hmm what is this strange magic?
        super(Employee, self).__init__(name)
        ## ??
        self.salary =salary

## Fish is-a object
class Fish(object):
    pass

## Salmon is-a Fish
class Salmon(Fish):
    pass

## Halibut is-a Fish
class Halibut(Fish):
    pass

## rover is-a dog
rover = Dog("Rover")

## satan is-a Cat
satan = Cat("Satan")

## mary is-a Person
mary = Person("Mary")

## mary has-a pet, satan is-a Cat
mary.pet = satan

## ??
frank = Employee("Frank", 12000)

## ??
frank.pet =rover

## ??
flipper =Fish()

## ??
crouse = Salmon()

## ??
harry = Halibut()

习题41涉及到的函数

https://www.runoob.com/python/python-func-str.html

https://www.runoob.com/python3/python3-string-strip.html

https://www.runoob.com/python3/python3-func-number-random.html

https://www.runoob.com/python3/python3-random-number.html

https://www.runoob.com/python/python-exercise-example94.html

https://www.runoob.com/python3/python3-string-capitalize.html

https://www.runoob.com/python3/python3-att-dictionary-keys.html

https://www.runoob.com/python3/python3-string-count.html

https://www.runoob.com/python3/python-copy-list.html

https://www.runoob.com/python3/python3-string-replace.html

https://www.runoob.com/python3/python3-func-number-shuffle.html