python - Python while 循环期间字符串连接的问题

Question

我最近开始尝试学习Python。作为一个学习项目，我一直在制作一个小型加密/解密程序。我遇到的问题是，我有一个 while 循环正在运行，因此可以从终端重新运行程序，而无需退出并重新加载程序。然而，这会以某种方式连接“james”变量，以便每次运行都会添加到 james 变量中。

由于我所做的所有尝试都失败了，如何将 james 变量清空？

#! /usr/bin/python

import random
import time

#This program will encrypt and decrypt a string (line of text or numbers)

#first we need a list of all the characters a-z, 0-9 and !-@
Alphabet = [' ','a','b', 'c', 'd','e','f', 'g', 'h','i', 'j', 'k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','1','2','3','4','5','6','7','8','9','0','!','"','£','$','%','^','&','*','(',')','@','?',',','\'','.',':' ]
#53 objects in list

#List to store each letter of the encrypted word
encryptedWord = []



#Now to create a function to search for a letter and performs the encryption
def encrypt(letter, Alphabet, encryptNo, operation):

    index = Alphabet.index(letter)#Finds the index of the given letter

    #These if statements determine whether the option for encryption or decryption
    #has been chosen and then performs the operation
    if operation == '1':    #Encryption
        if ((index + encryptNo)<=53):
            newIndex = index + encryptNo
        else:
            newIndex = ((index + encryptNo)-53)

    else:                   #Decryption
        if ((index - encryptNo)>=0):
            newIndex = index - encryptNo
        else:
            newIndex = ((index - encryptNo)+53)

    retLetter = Alphabet[newIndex]
    return (retLetter)

def displayIntro():
    print ('Welcome to the encryption and decryption tool')
    print ('Encrypting some text translates the text into a secret code.')
    print ('Decrypting a secret code will translate it back into normal text')
    print ()
    print ('---------------------------------------------------------------------------')
    print ()
    operation = input('Select from the options below.\n 1= Encryption\n 2= Decryption\n Choice: ')

    encryptNo = int(input('Type your encryption Factor (1-25): '))

    wordToEncrypt = input('Type the word you would like to encrypt: ')
    return (operation, encryptNo, wordToEncrypt)


#now to the program, The playagain while loops is meant to allow for multiple running of the file.
james = ''
playAgain = 'yes'
while playAgain == 'yes' or playAgain == 'y':
    operation, encryptNo, wordToEncrypt = displayIntro()

    #The next line splits the word string into seperate letters and fills a list called dave with each letter.
    dave = [wordToEncrypt[i:i+1] for i in range(0, len(wordToEncrypt), 1)]

    #Now I loop through the dave list sending the encrypt function each letter one at a time and returning the 
    #encrypted/decrypted letter
    i=0
    while i<=(len(dave)-1):
        letter = dave[i]
        encryptedLetter = encrypt(letter, Alphabet, encryptNo, operation)
        encryptedWord.extend([encryptedLetter])
        i = i+1

    #This is where My problem occurs. Each time I run through the while loop it is
        #concatonating the james variable with what it was the previous run through.
        #the del james doesnt seem to work either :(
    del james
    james = ''.join(encryptedWord)
    print ()
    if operation == '1':
        print ('Your secret code is: ',james)
    else:
        print ('Your code said: ', james)


    print ()
    print ('----------------------------------------------------------------------')
    print ()
    print ('do you want to play again? (yes or no)')
    playAgain = 'no'
    playAgain = input()

运行此程序使用加密系数 10 来加密单词 john，将返回单词 tyrx。如果您选择"is"再次播放，然后解密 tyrx，它将返回 tyrxjohn。

希望我能说清楚。

Answer 1

1. 您正在扩展 encryptedWord[] 而不重新初始化它。
2. 您没有在循环开始或结束时将 james 初始化为空白。

解决方案:

在循环开始时将 james 和 ecnryptedWord[] 都初始化为空白。