我正在做 edx 问题集 5，我在我的代码中偶然发现了一个问题：
# 6.00x Problem Set 5
#
# Part 1 - HAIL CAESAR!
import string
import random
WORDLIST_FILENAME = "words.txt"
# -----------------------------------
# Helper code
# (you don't need to understand this helper code)
def loadWords():
"""
Returns a list of valid words. Words are strings of lowercase letters.
Depending on the size of the word list, this function may
take a while to finish.
"""
print "Loading word list from file..."
inFile = open(WORDLIST_FILENAME, 'r')
wordList = inFile.read().split()
print " ", len(wordList), "words loaded."
return wordList
def isWord(wordList, word):
"""
Determines if word is a valid word.
wordList: list of words in the dictionary.
word: a possible word.
returns True if word is in wordList.
Example:
>>> isWord(wordList, 'bat') returns
True
>>> isWord(wordList, 'asdf') returns
False
"""
word = word.lower()
word = word.strip(" !@#$%^&*()-_+={}[]|\\:;'<>?,./\"")
return word in wordList
def randomWord(wordList):
"""
Returns a random word.
wordList: list of words
returns: a word from wordList at random
"""
return random.choice(wordList)
def randomString(wordList, n):
"""
Returns a string containing n random words from wordList
wordList: list of words
returns: a string of random words separated by spaces.
"""
return " ".join([randomWord(wordList) for _ in range(n)])
def randomScrambled(wordList, n):
"""
Generates a test string by generating an n-word random string
and encrypting it with a sequence of random shifts.
wordList: list of words
n: number of random words to generate and scamble
returns: a scrambled string of n random words
NOTE:
This function will ONLY work once you have completed your
implementation of applyShifts!
"""
s = randomString(wordList, n) + " "
shifts = [(i, random.randint(0, 25)) for i in range(len(s)) if s[i-1] == ' ']
return applyShifts(s, shifts)[:-1]
def getStoryString():
"""
Returns a story in encrypted text.
"""
return open("story.txt", "r").read()
# (end of helper code)
# -----------------------------------
#
# Problem 1: Encryption
#
def buildCoder(shift):
"""
Returns a dict that can apply a Caesar cipher to a letter.
The cipher is defined by the shift value. Ignores non-letter characters
like punctuation, numbers and spaces.
shift: 0 <= int < 26
returns: dict
"""
dict={}
upper = string.ascii_uppercase
lower = string.ascii_lowercase
for l in range(len(upper)):
dict[upper[l]] = upper[(l+shift)%len(upper)]
for l in range(len(lower)):
dict[lower[l]] = lower[(l+shift)%len(lower)]
return dict
def applyCoder(text, coder):
"""
Applies the coder to the text. Returns the encoded text.
text: string
coder: dict with mappings of characters to shifted characters
returns: text after mapping coder chars to original text
"""
new_text=''
for l in text:
if not(l in string.punctuation or l == ' ' or l in str(range(10))):
new_text += coder[l]
else:
new_text += l
return new_text
def applyShift(text, shift):
"""
Given a text, returns a new text Caesar shifted by the given shift
offset. Lower case letters should remain lower case, upper case
letters should remain upper case, and all other punctuation should
stay as it is.
text: string to apply the shift to
shift: amount to shift the text (0 <= int < 26)
returns: text after being shifted by specified amount.
"""
### TODO.
### HINT: This is a wrapper function.
coder=buildCoder(shift)
return applyCoder(text,coder)
#
# Problem 2: Decryption
#
def findBestShift(wordList, text):
"""
Finds a shift key that can decrypt the encoded text.
text: string
returns: 0 <= int < 26
"""
### TODO
wordsFound=0
bestShift=0
for i in range(26):
currentMatch=0
encrypted=applyShift(text,i)
lista=encrypted.split(' ')
for w in lista:
if isWord(wordList,w):
currentMatch+=1
if currentMatch>wordsFound:
currentMatch=wordsFound
bestShift=i
return bestShift
def decryptStory():
"""
Using the methods you created in this problem set,
decrypt the story given by the function getStoryString().
Use the functions getStoryString and loadWords to get the
raw data you need.
returns: string - story in plain text
"""
text = getStoryString()
bestMatch = findBestShift(loadWords(), text)
return applyShift(text, bestMatch)
#
# Build data structures used for entire session and run encryption
#
if __name__ == '__main__':
wordList = loadWords()
decryptStory()
s = 'Pmttw, ewztl!'
print findBestShift(wordList, s)
print decryptStory()
问题是该程序的单个模块与解密故事不同。那段代码有什么问题？