如何从艰苦的学习Python中阅读练习41的代码？

Question

我试图理解下面的代码，并且遇到了困难。有人可以回答几个问题来帮助我理解吗？

我知道PHRASES（变量）包含字典，因此“类%%%（%%%）”映射为“使名为%%%的类为-a %%%”。

这些行（第2-13行）是否也实际上是在创建类，还是就像“字符串”一样？因为它看起来可能正在创建类，但是我不确定。

我也知道%%%， * 和@@@实际上会被代码中某些地方的实际单词替换，但是不知道如何或在哪里，因为它们看上去都如此令人困惑。

那么，有人可以帮助我吗？谢谢！

1 PHRASES = {
2 "class %%%(%%%):":
3  "Make a class named %%% that is-a %%%.",
4 "class %%%(object):\n\tdef __init__(self, ***)" :
5  "class %%% has-a __init__ that takes self and *** parameters.",
6 "class %%%(object):\n\tdef ***(self, @@@)":
7  "class %%% has-a function named *** that takes self and @@@ parameters.",
8 "*** = %%%()":
9  "Set *** to an instance of class %%%.",
10 "***.***(@@@)":
11 "From *** get the *** function, and call it with parameters self, @@@.",
12 "***.*** = '***'":
13  "From *** get the *** attribute and set it to '***'."
14 }

哦，这是您需要时的全部代码：

import random
from urllib import urlopen
import sys

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

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

PHRASE_FIRST = False
if len(sys.argv) == 2 and sys.argv[1] == "english":
    PHRASE_FIRST = True

for word in urlopen(WORD_URL).readlines():
    WORDS.append(word.strip())


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[:]

        for word in class_names:
            result = result.replace("%%%", word, 1)

        for word in other_names:
            result = result.replace("***", word, 1)

        for word in param_names:
            result = result.replace("@@@", word, 1)

        results.append(result)

    return results


try:
    while True:
        snippets = 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

            raw_input("> ")
            print "ANSWER:  %s\n\n" % answer
except EOFError:
    print "\nBye"

Answer 1

这些行正在创建一个字符串字典，这些字典的键的语法与有效的Python类定义相似，而值则描述它们的作用。

例如， "class %%%(object):\n\tdef __init__(self, ***)"

成为

class %%%(object):
    def __init__(self, ***)

我也知道%%%，***和@@@真正能拿到的实际词语的代码替换某个地方，但不知道如何或在哪里，因为它只是一切看起来如此混乱。

这一点很明显，例如：

result = result.replace("@@@", word, 1)

这些单词是从中获取的WORD_URL = "http://learncodethehardway.org/words.txt"。