新手一枚，買的書是教Python2，想學Python3，ex41一直報錯，上網查後發現主要是三個問題:

1. Python3中urllib庫發生變化

2. Python3中嚴格區分str和bytes，29行遍及讀取網頁上的單詞，word為bytes，不能作為replace()的第二個引數

3. Python3中dict.keys返回的不是列表，需要用list()處理

下面貼出可以python3.6.5可以執行的程式碼：

import random
from urllib.request import urlopen #改成python3中的方法
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 '***'."
}

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

# load up the word from the website
for word in urlopen(WORD_URL).readlines():
    word = word.decode() #bytes變為str
    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[:]

        # fake class name
        for word in class_names:
            result = result.replace("%%%", word, 1)

        # fake other name
        for word in other_names:
            result = result.replace("***", word, 1)

        # fake parameter name
        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()) #變為列表
        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("ANSWER:  %s\n\n" % answer)
except EOFError:
    print("\nBye")