Python - 凯撒密码 [英] Python - Caesar Cipher

问题描述

我是 Python 新手，我想尝试制作一个凯撒密码，并且可以对我的代码使用一些帮助.它看起来像这样:

I'm new to Python and thought I'd try to make a Caesar cipher and could use some help with my code. It looks like this:

def cipher(input):
    input = input.lower()  #don't mind capital letters
    output = []
    alphabet = 'abcdefghijklmnopqrstuvwxyz'
    steps = int(raw_input('How many steps? >> '))

    for i in input:
        if i == ' ':  #for space
            output.append(' ')
        else:
            pos = alphabet.index(i) + steps
            if pos >= 25:  #for out-of-range
                pos -= 26

        output.append(alphabet[pos])

    print 'The ciphered message: ', ''.join(output)


input = raw_input('Write your message. >> ')
cipher(input)

当涉及到空间时，它似乎有点作用，但并不完全.

It seems to work a bit, but not fully, when it comes to spaces.

这是我得到的:

Write your message. >> abc abc
How many steps? >> 1
The ciphered message:  bcd dbcd

我不太明白输出中额外的字母(在本例中为 d)从何而来.

I don't quite understand where the extra letter (d, in this case) in the output comes from.

感谢您的帮助.

推荐答案

您的缩进不正确:

for i in input:
    if i == ' ':  #for space
        output.append(' ')
    else:
        pos = alphabet.index(i) + steps
        if pos >= 25:  #for out-of-range
            pos -= 26

    output.append(alphabet[pos]) # note here

您append 到output 无论i 是否为空格.如果第一个字符是空格(NameError，因为 pos 尚未分配)，这将完全中断，但只会导致字符串中其他地方的重复.

You append to the output whether or not i is a space. This would break completely if the first character was a space (NameError, as pos is not yet assigned), but just causes repeats elsewhere in the string.

更改为:

for i in input:
    if i == ' ':  #for space
        output.append(' ')
    else:
        pos = alphabet.index(i) + steps
        if pos >= 25:  #for out-of-range
            pos -= 26
        output.append(alphabet[pos]) # now inside 'else'

注意你也可以简化你的out-of-range:

Note you can also simplify your out-of-range:

pos = (alphabet.index(i) + steps) % 26

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