Python 帮助 - 学习 Python The Hard Way 练习 41 "phrase = PHRASES[snippet]"

Question

我正在学习python——这是我学习的第一种编程语言。我对其中一行代码有点困惑。完整代码也可以在http://learnpythonthehardway.org/book/ex41.html

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):ntdef __init__(self, ***)" :
    "class %%% has-a __init__ that takes self and *** parameters.",
"class %%%(object):ntdef ***(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:  %snn" % answer
except EOFError:
print "nBye"

这是我不太理解的倒数第11行代码：phrase = PHRASES[snippet]。既然for snippet in snippets:中的代码片段是通过随机打乱的PHRASES列表的键循环的，为什么代码不能简单地是phrase = snippet呢。提前感谢您的帮助。干杯-Darren

Answer 1

获取字典中键"snippet"的值