import string ### DO NOT MODIFY THIS FUNCTION ### 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...') # inFile: file in_file = open(file_name, 'r') # line: string line = in_file.readline() # word_list: list of strings word_list = line.split() print(' ', len(word_list), 'words loaded.') in_file.close() return word_list ### DO NOT MODIFY THIS FUNCTION ### 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 Example: >>> is_word(word_list, 'bat') returns True >>> is_word(word_list, 'asdf') returns False ''' word = word.lower() word = word.strip(" !@#$%^&*()-_+={}[]|\:;'<>?,./\"") return word in word_list ### DO NOT MODIFY THIS FUNCTION ### 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): ### DO NOT MODIFY THIS METHOD ### def __init__(self, text): ''' Initializes a Message object text (string): the message's text a Message object has two attributes: self.message_text (string, determined by input text) self.valid_words (list, determined using helper function load_words ''' self.message_text = text self.valid_words = load_words(WORDLIST_FILENAME) ### DO NOT MODIFY THIS METHOD ### def get_message_text(self): ''' Used to safely access self.message_text outside of the class Returns: self.message_text ''' return self.message_text ### DO NOT MODIFY THIS METHOD ### 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 should have 52 keys of all the uppercase letters and all the lowercase letters only. 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). ''' cipher = {} lower_alpha = string.ascii_lowercase upper_alpha = string.ascii_uppercase # Both strings have the same length, and same shift, so, loop through # both together, to avoid two loops for i in range(len(lower_alpha)): new_idx = lower_alpha.index(lower_alpha[i]) + shift if ((len(lower_alpha)) - new_idx) <= 0: new_idx = abs((len(lower_alpha)) - new_idx) cipher[lower_alpha[i]] = lower_alpha[new_idx] cipher[upper_alpha[i]] = upper_alpha[new_idx] return cipher 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 ''' cipher = self.build_shift_dict(shift) new_msg = '' for i in self.get_message_text(): if i in cipher.keys(): new_msg += cipher[i] else: new_msg += i return new_msg 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 A PlaintextMessage object inherits from Message and has five attributes: self.message_text (string, determined by input text) self.valid_words (list, determined using helper function load_words) self.shift (integer, determined by input shift) self.encrypting_dict (dictionary, built using shift) self.message_text_encrypted (string, created using shift) Hint: consider using the parent class constructor so less code is repeated ''' Message.__init__(self, text) self.shift = shift self.encrypting_dict = self.build_shift_dict(shift) self.message_text_encrypted = self.apply_shift(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 self.encrypting_dict.copy() 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 ''' PlaintextMessage.__init__(self, self.get_message_text(), shift) class CiphertextMessage(Message): def __init__(self, text): ''' Initializes a CiphertextMessage object text (string): the message's text a CiphertextMessage object has two attributes: self.message_text (string, determined by input text) self.valid_words (list, determined using helper function load_words) ''' Message.__init__(self, text) def decrypt_message(self): ''' Decrypt self.message_text by trying every possible shift value and find the "best" one. We will define "best" as the shift that creates the maximum number of real words when we use apply_shift(shift) on the message text. If s is the original shift value used to encrypt the message, then we would expect 26 - s to be the best shift value for decrypting it. Note: if multiple shifts are equally good such that they all create the maximum number of you may choose any of those shifts (and their corresponding decrypted messages) to return Returns: a tuple of the best shift value used to decrypt the message and the decrypted message text using that shift value ''' best_shift = 0 best_count = 0 for i in range(0, 26): cur_text = self.apply_shift(i) wlist = cur_text.split(' ') count = 0 for w in wlist: if is_word(self.valid_words, w): count += 1 if count >= best_count: best_count = count best_shift = i return (best_shift, self.apply_shift(best_shift)) #Example test case (PlaintextMessage) plaintext = PlaintextMessage('hello', 2) print('Expected Output: jgnnq') print('Actual Output:', plaintext.get_message_text_encrypted()) #Example test case (CiphertextMessage) ciphertext = CiphertextMessage('jgnnq') print('Expected Output:', (24, 'hello')) print('Actual Output:', ciphertext.decrypt_message()) def decrypt_story(): cipherMsg = CiphertextMessage(get_story_string()) return cipherMsg.decrypt_message()