Python 2 凯撒密码

Question

我的问题是如何改进这段代码，让它能够适应任意长度的输入信息。目前，这段代码要求信息必须是5个字母。我想改进它，让任何长度的信息都可以输入，并且加密功能都能正常工作。非常感谢大家的帮助。:-) 下面是代码！

#Enter your message
message=raw_input('Enter your message here. Make sure to use all CAPS througout your message and leave no spaces in between words.')
length=len(message)
print 'The length of your message is ',length

#This statement is a possible idea to let the program know how many letters it will be need to shift. But I don't know how to actually do this.
print chr(length+64)
#Indexes letters out of message.
A=message[length-length]
B=message[length-length+1]
C=message[length-length+2]
D=message[length-length+3]
E=message[length-length+4]

#Shifts letters and accounts for shifting XYZ to ABC. 
def shift(x):
    if ord(x)+3==91:
        return 65
    if ord(x)+3==92:
        return 66
    if ord(x)+3==93:
        return 67
    else:
        return ord(x)+3

a2=shift(A)
b2=shift(B)
c2=shift(C)
d2=shift(D)
e2=shift(E)


#Converts shifted ordinals back to characters
def convert(x):
    return chr(x)
first=convert(a2)
second=convert(b2)
third=convert(c2)
fourth=convert(d2)
fifth=convert(e2)

#Prints resultant characters
print first,second,third,fourth,fifth

Answer 1

这里有一个简单的凯撒密码程序，是用Python 3写的，应该不难改写成Python 2的版本：

import string

def main():
    key = 5
    table = str.maketrans(string.ascii_letters,
                          string.ascii_lowercase[key:] +
                          string.ascii_lowercase[:key] +
                          string.ascii_uppercase[key:] +
                          string.ascii_uppercase[:key])
    plaintext = input('Please enter a phrase: ')
    ciphertext = plaintext.translate(table)
    print('Your encrypted phrase is:', ciphertext)

if __name__ == '__main__':
    main()

Answer 2

使用两个for循环，一个用来遍历每个字符，另一个用来将字符移动指定的次数。我们用一个叫upper()的函数来移动字符。

def upper(char):
    from string import ascii_letters as _all
    if char == ' ':
        return ' '
    return _all[_all.index(char)+1] if char != 'Z' else 'a'

def shift(message, key):
    temp = []
    for i in message:
        char = i
        for k in range(key):
            char = upper(char)
        temp.append(char)
    return ''.join(temp)

message=raw_input('Enter your message here: ')
key = int(raw_input('Enter the desired key: '))
length=len(message)
print 'The length of your message is', length

print 'Your encrypted message is {0}'.format(shift(message, key))

这个过程是这样的：

bash-3.2$ python caesar.py
Enter your message here: This works WITH or without CAPS
Enter the desired key: 10
The length of your message is 31
Your encrypted message is drsC GyBuC gSdR yB GsDryED MKZc
bash-3.2$ 

Answer 3

凯撒密码在Python 2中是内置的;

In [6]: 'The Caesar cipher is built-in.'.encode('rot13')
Out[6]: 'Gur Pnrfne pvcure vf ohvyg-va.'

正如你所看到的，这种编码只对字母有效，并且对大写和小写字母都适用。

但是如果你想去掉空格并把所有字母变成大写，Python也能做到这一点;

In [9]: 'this is a string'.translate(None, ' \t')
Out[9]: 'thisisastring'

In [10]: 'this is a string'.translate(None, ' \t').upper()
Out[10]: 'THISISASTRING'

In [11]: 'this is a string'.translate(None, ' \t').upper().encode('rot13')
Out[11]: 'GUVFVFNFGEVAT'

或者用另一种方式;

In [15]: ''.join('this is a string'.split()).upper().encode('rot13')
Out[15]: 'GUVFVFNFGEVAT'

Answer 4

import string
shift_amt = 13
alphabet_lc = string.ascii_lowercase
shifted_lc = alphabet_lc[shift_amt:]+alphabet_lc[:shift_amt]

alphabet_uc = alphabet_lc.upper()  
shifted_uc = shifted_lc.upper()
trans_tab = string.maketrans(alphabet_lc+alphabet_uc,shifted_lc+shifted_uc)



message = "Encode Me To a new MessaGez!"
print message.translate(trans_tab)

这是一种在Python2中实现的方法。