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import string
def load_words(file_name):
'''
file_name (string): the name of the file containing
the list of words to load.
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...')
in_file = open(file_name, 'r')
line = in_file.readline()
word_list = line.split()
print(' ', len(word_list), 'words loaded.')
in_file.close()
return word_list
def is_word(word_list, word):
'''
Determines if word is a valid word, ignoring
capitalization and punctuation
word_list (list): list of words in the dictionary.
word (string): a possible word.
Returns: True if word is in word_list, False otherwise
'''
word = word.lower()
word = word.strip(" [email protected]#$%^&*()-_+={}[]|\:;'<>?,./\"")
return word in word_list
def get_story_string():
"""
Returns: a joke in encrypted text.
"""
f = open("story.txt", "r")
story = str(f.read())
f.close()
return story
WORDLIST_FILENAME = 'words.txt'
class Message(object):
def __init__(self, text):
'''
Initializes a Message object
text (string): the message's text
'''
self.message_text = text
self.valid_words = load_words(WORDLIST_FILENAME)
def get_message_text(self):
'''
Used to safely access self.message_text outside of the class
Returns: self.message_text
'''
return self.message_text
def get_valid_words(self):
'''
Used to safely access a copy of self.valid_words outside of the class
Returns: a COPY of self.valid_words
'''
return self.valid_words[:]
def build_shift_dict(self, shift):
'''
Creates a dictionary that can be used to apply a cipher to a letter.
The dictionary maps every uppercase and lowercase letter to a
character shifted down the alphabet by the input shift. The dictionary
has 52 keys of all the uppercase letters and all the lowercase
letters.
shift (integer): the amount by which to shift every letter of the
alphabet. 0 <= shift < 26
Returns: a dictionary mapping a letter (string) to
another letter (string).
'''
shiftedLowercase = list(string.ascii_lowercase[shift:] +
string.ascii_lowercase[:shift])
shiftedUppercase = list(string.ascii_uppercase[shift:] +
string.ascii_uppercase[:shift])
shiftedAlphabet = shiftedLowercase + shiftedUppercase
return dict(zip(string.ascii_letters, shiftedAlphabet))
def apply_shift(self, shift):
'''
Applies the Caesar Cipher to self.message_text with the input shift.
Creates a new string that is self.message_text shifted down the
alphabet by some number of characters determined by the input shift.
shift (integer): the shift with which to encrypt the message.
0 <= shift < 26
Returns: the message text (string) in which every character is shifted
down the alphabet by the input shift
'''
return ''.join([self.build_shift_dict(shift)[x] if x in
string.ascii_letters else x for x in self.message_text
])
class PlaintextMessage(Message):
def __init__(self, text, shift):
'''
Initializes a PlaintextMessage object.
text (string): the message's text
shift (integer): the shift associated with this message
'''
Message.__init__(self, text)
self.shift = shift
self.encrypting_dict = Message.build_shift_dict(self, shift)
self.message_text_encrypted = Message.apply_shift(self, shift)
def get_shift(self):
'''
Used to safely access self.shift outside of the class
Returns: self.shift
'''
return self.shift
def get_encrypting_dict(self):
'''
Used to safely access a copy self.encrypting_dict outside of the class
Returns: a COPY of self.encrypting_dict
'''
return dict(self.encrypting_dict)
def get_message_text_encrypted(self):
'''
Used to safely access self.message_text_encrypted outside of the class
Returns: self.message_text_encrypted
'''
return self.message_text_encrypted
def change_shift(self, shift):
'''
Changes self.shift of the PlaintextMessage and updates other
attributes determined by shift (ie. self.encrypting_dict and
message_text_encrypted).
shift (integer): the new shift that should be associated with
this message. 0 <= shift < 26
Returns: nothing
'''
self.shift = shift
self.encrypting_dict = self.build_shift_dict(shift)
self.message_text_encrypted = self.apply_shift(shift)
class CiphertextMessage(Message):
def __init__(self, text):
'''
Initializes a CiphertextMessage object
text (string): the message's text
'''
Message.__init__(self, text)
def decrypt_message(self):
'''
Decrypt self.message_text by trying every possible shift value
and find the "best" one. The "best" one is defined as the shift that
creates the maximum number of real words when apply_shift(shift) is
used on the message text.
Returns: a tuple of the best shift value used to decrypt the message
and the decrypted message text using that shift value
'''
countValidWords = 0
bestShiftValue = 0
for i in range(27):
decryptWordsList = self.apply_shift(i).split()
countValidWords = ([1 for x in decryptWordsList if
is_word(self.valid_words, x)]).count(1)
if countValidWords > bestShiftValue:
bestShiftValue = i
return (bestShiftValue, self.apply_shift(bestShiftValue))
def decrypt_story():
'''
This function simply decrypts the previously encrypted story
inside story.txt
'''
story = get_story_string()
encryptedStory = CiphertextMessage(story)
decryptedStory = encryptedStory.decrypt_message()
return decryptedStory
print(decrypt_story())