练习41：学着去说面向对象

Posted 2020-12-19 luoxun

一 词汇训练

• 类（class）：告诉python创建一个新类型的东西。（Tell python to make a new type of thing）.
• 对象（object）：两种含义：最基本类型的东西，任何实例。（the most basic type of thing,and any instance of something）。
• 实例（instance）：当你告诉python创建一个类的时候你所得到的东西。（What you get when you tell pythong to create a class）.
• def：你如何在类里面定义一个函数。（How you define a function inside a class）。
• self：在一个类的函数里面，self是被访问的实例/对象的一个变量。（inside the functions in a class,self is a variable for the instance/object being accessed）。
• 继承（inheritance）：关于一个类能从另一个类那里继承它的特征的概念，很像你和你的父母。（The concept that one class can inhert traits from other class,much like you and your parents）。
• 组合（composition）：关于一个类可以由其它一些类构成的概念，很像一辆车包含几个轮子。（The concept that a class can be composed of other classes as parts,much like how a car has wheels）。
• 属性（attribute）：类所拥有的从组合那里得到的特性，通常是变量。（A property classes have that are from composition and are usually variables）。
• is-a：一种用来表达某物继承自一种东西的表述，就像“三文鱼是一种鱼”。（A phrase to say that something are from inherits from another,as in a "salmon" is a "fish"）
• has-a：一种用来表达某物是由一些东西组成或具有某种特性的表述，就像“三文鱼有一个嘴巴。”（A phrase to say that something is composed of other things or has a trait,as in "a salmon has-a mouth."）

二 短语训练

• class X(Y) ：创建一个名为 X 并继承自 Y 的类。(“Make a class named X that is-a Y.”)
• class X(object): def __init__(self, J)：类 X 有一个带有 self 和 J 参数的 __init__ 函数。(“class X has-a __init__ that takes self and J parameters.”)
• class X(object): def M(self, J) ：类 X 有一个带有 self 和 J 参数的 M 函数。(“class X has-a function named M that takes self and J parameters.”)
• foo = X() ：设 foo 为类 X 的一个实例。(“Set foo to an instance of class X.”)
• foo.M(J)  从 foo 那里获取 M 函数，并用 self 和 J 参数来调用它。(“From foo, get the M function, and call it with parameters self, J.”)
• foo.K = Q  从 foo 那里获取 K 属性，并设它为 Q。(“From foo, get the K attribute, and set it to Q.”)

三 代码

1 相关知识

2 代码

 1 import random
 2 from urllib.request import urlopen
 3 import sys
 4 
 5 WORD_URL = "http://learncodethehardway.org/words.txt"
 6 WORDS = []
 7 
 8 PHRASES = {
 9     "class %%%(%%%):":
10         "Make a class named %%% that is-a %%%.",
11     "class %%%(object):
	def __init__(self,***)":
12         "class %%% has-a __init__ that takes self and *** params.",
13     "class %%%(object):
	def ***(self,@@@)":
14         "class %%% has-a function *** that takes self and @@@ params.",
15     "*** = %%%()":
16             "Set *** to an instance of class %%%.",
17     "***.***(@@@)":
18             "From *** get the *** function,call it with params self @@@.",
19     "***.*** = ‘***‘":
20             "From *** get the *** attribute and set it to ‘***‘."
21 }
22 
23 # do they want to drill phrases first
24 if len(sys.argv) == 2 and sys.argv[1] == "english":
25     PHRASE_FIRST = True
26 else:
27     PHRASE_FIRST = False
28 
29 # load up the words from the website
30 for word in urlopen(WORD_URL).readlines():
31     WORDS.append(str(word.strip(),encoding="utf-8"))
32 
33 def convert(snippet,phrase):
34     class_names = [w.capitalize() for w in
35     random.sample(WORDS,snippet.count("%%%"))]
36     other_names = random.sample(WORDS,snippet.count("***"))
37     results = []
38     param_names = []
39     
40     for i in range(0,snippet.count("@@@")):
41         param_count = random.randint(1,3)
42         para_names.append(‘,‘.join(
43             random.sample(WORDS,param_count)))
44     
45     for sentence in snippet,phrase:
46         result = sentence[:]
47         
48         # fake class names
49         for word in class_names:
50             result = result.replace("%%%",word,1)
51         
52         # fake other names
53         for word in other_names:
54             result = result.replace("***",word,1)
55         
56         # fake parameter lists
57         for word in param_names:
58             result = result.replace("@@@",word,1)
59         
60         results.append(result)
61     return results
62 
63 # keep going until they hit CTRL-D
64 try:
65     while True:
66         snippets = list(PHRASES.keys())
67         random.shuffle(snippets)
68         
69         for snippet in snippets:
70             phrase = PHRASES[snippet]
71             question,answer = convert(snippet,phrase)
72             if PHRASE_FIRST:
73                 question,answer = answer,question
74             
75             print(question)
76             
77             input("> ")
78             print(f"ANSWER:{answer}

")
79 except EOFError:
80     print("
Bye")