Python filter/lambda [duplicate]

问题

Trying to create a keyword cipher and Ive come across this,I know that it makes the string upper case and remove things like spaces commas and parentheses.I've tried removing it and my code doesnt work, I just want to know how I can remove this successfully

from itertools import   starmap,cycle                                                           

def encrypt(message, key):                                                                     

    # convert to uppercase.                                                                    
    # strip out non-alpha characters.                                                          
    message = filter(lambda _: _.isalpha(), message.upper())                                   

    # single letter encrpytion.                                                                
    def enc(c,k): return chr(((ord(k) + ord(c)) % 26) + ord('A'))                              

    return "".join(starmap(enc, zip(message, cycle(key))))                                     

def decrypt(message, key):                                                                     

    # single letter decryption.                                                                
    def dec(c,k): return chr(((ord(c) - ord(k)) % 26) + ord('A'))                              

    return "".join(starmap(dec, zip(message, cycle(key))))

text = input("Enter the message you want to crypt: ")     
key =  input("Enter the key you would like to use: ")                                                                       

encr = encrypt(text, key)                                                                      
decr = decrypt(encr, key)                                                                      

print (text)                                                                                     
print (encr)                                                                                   
print (decr)

回答1:

Your error can be observed by looking at this line:

def enc(c,k): return chr(((ord(k) + ord(c)) % 26) + ord('A'))

This function exploits character codes to encrypt the result. Since it uses modulo 26, and adds ord('A') it is specialized for upper case letters. One way to rewrite the encryption/decryption if you don't mind unreadable encrypted strings is:

from itertools import cycle

def encrypt(message,key):
    def encryptLetter(letterKey):
        letter,key=letterKey
        return chr(ord(letter)+ord(key))
    keySeq=cycle(key)
    return "".join(map(encryptLetter,zip(message,keySeq)))

def decrypt(message,key):
    def decryptLetter(letterKey):
        letter,key=letterKey
        return chr(ord(letter)-ord(key))
    keySeq=cycle(key)
    return "".join(map(decryptLetter,zip(message,keySeq)))

Obviously this isn't secure at all...

来源：https://stackoverflow.com/questions/28771396/python-filter-lambda

标签

python

encryption

filter

lambda

keyword