python-2.7 - Python Help - Learn Python The Hard Way 练习 41 “phrase = PHRASES[snippet]”

Question

我正在学习 python - 这是我正在学习的第一门编程语言。我对一行代码有点困惑。完整的代码也可以在http://learnpythonthehardway.org/book/ex41.html找到

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 '***'."
}

# 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 words from the website
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[:]

    # fake class name
    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 lists
    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 = PHRASES.keys()
    # returns a randomly shuffled dictionary keys list
    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"

这是我不太明白的从底部开始的第 11 行代码：phrase = PHRASES[snippet]. 既然代码片段在for snippet in snippets:循环随机打乱的 PHRASES 列表的键，为什么代码不能简单地是phrase = snippet. 提前感谢您的帮助。干杯 - 达伦

Answer 1

获取字典中键“snippet”的值