Python 朱利叶斯·凯撒密码程序

Question

我正在尝试制作朱利叶斯·凯撒密码程序，但通过在句子的开头和结尾添加一个随机字母来添加一个扭曲。由于某种原因，当我输入长字符串时，打印时该字符串的一部分会丢失。我正在使用 python 3。有人可以解释如何解决这个问题以及为什么会发生这种情况吗？谢谢

import random
alpha = 'abcdefghijklmnopqrstuvwxyz'
alphaupper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'


def encode(cleartext):
    global alpha
    global alphaupper
    words = cleartext
    cyphertext = ""
    for char in words:
        if char in alphaupper:
            newpos = (alphaupper.find(char) + 13) % 26
            cyphertext += alphaupper[newpos]
        elif char in alpha:
            newpos = (alpha.find(char) + 13) % 26
            cyphertext += alpha[newpos]
        else:
            cyphertext += char

    cyphertext = alpha[random.randrange(len(alpha) - 1)] + cyphertext + alpha[random.randrange(len(alpha) - 1)]
    return cyphertext


def decode(cleartext):
    global alpha
    global alphaupper
    words = cleartext.replace(cleartext[len(cleartext) - 1], "")
    words = words.replace(words[0], "")
    cyphertext = ""
    for char in words:
        if char in alphaupper:
            newpos = (alphaupper.find(char) + 13) % 26
            cyphertext += alphaupper[newpos]
        elif char in alpha:
            newpos = (alpha.find(char) + 13) % 26
            cyphertext += alpha[newpos]
        else:
            cyphertext += char
    return cyphertext


print("Julias Ceasar 13 letter shift")


def men():
    words = input("Would you like to decode or encode: ")
    if "decode" in words:
        words = input("What would you like to decode: ")
        print(decode(words))
        print('\n')
        men()
    elif "encode" in words:
        words = input("What would you like to encode: ")
        print(encode(words))
        print('\n')
        men()
    else:
        print("Could not understand please try again")
        print('\n')
        men()


if __name__ == "__main__":
    men()

输出:

Julias Ceasar 13 letter shift
Would you like to decode or encode: encode
What would you like to encode: This program deletes parts of this string for some reason

编码:

yGuvf cebtenz qryrgrf cnegf bs guvf fgevat sbe fbzr ernfbas

解码:

Would you like to decode or encode: decode
What would you like to decode: yGuvf cebtenz qryrgrf cnegf bs guvf fgevat sbe fbzr ernfbas

最终解码的句子:

This program deletes parts o this string or some reason


Would you like to decode or encode: 

Answer 1

看起来问题是，在解码时，你这样做

words = cleartext.replace(cleartext[len(cleartext) - 1], "")
words = words.replace(words[0], "")

str.replace如果您不包含可选的第三个 count 参数，则替换所有出现的情况。这意味着您删除的字符数量超出了您的预期。

如果您只想删除字符串中的第一个和最后一个字符，您可以执行类似的操作

words = cleartext[1:-1]

这更干净，因为您实际上并不关心第一个和最后一个字符是什么，您只是希望它们消失。