Encryption Python - encrypting a string

Question

Using this program to take out spaces, punctuation, and make letters lower case...

def pre_process(s):
    s= s.replace("'","")
    s= s.replace('.','')
    s= s.lower()
    s= s.replace(" ","")
    return s

How can I encrypt a message (s) so that the letters each shift by an amount equal to the corresponding letter in the alphabet? ex) 'm' shifted 5 becomes 'r' but 'w' shifted 5 becomes 'b'?

possible duplicate of [How to make shift('w','f') return 'b'?](http://stackoverflow.com/questions/28756582/how-to-make-shiftw-f-return-b) — Cristian Ciupitu, Feb 27 '15 at 19:26

score 1 · Answer 1 · answered Feb 27 '15 at 05:32

You have to do some ord and chr tricks to do what you want. Basically, these two functions return the integer representation of your letters, and outputs the corresponding letter of the integer representation, respectively.

def pre_process(s):
    s= s.replace("'","")
    s= s.replace('.','')
    s= s.lower()
    s= s.replace(" ","")

    mystring = ""
    for letter in s:
        shift = 5
        r = ord(letter)+shift
        if (r > ord('z')):
            r -= 26
        mystring += (chr(r))
    return mystring

Damn beat me to it !! Very quick, was typing almost the same thing — Illusionist, Feb 27 '15 at 05:32

score 0 · Accepted Answer · answered Feb 27 '15 at 05:50

0

This may be helpful to you...Just change the value of shifter in encrypt function to get the corresponding shift

def shift(char,shift_by):
    val=ord(char) #gives ascii value of charecter
    val+=shift_by
    if(val>122):
        val=97+(val-122-1)
    return(chr(val))

def encrypt_string(str):
    shifter=2 #change to value of shifter here
    encrypted_string=""
    for i in str :
        if( (ord(i)>=97) and (ord(i)<=122) ):
            i=shift(i,shifter)
        encrypted_string+=i
    return(encrypted_string)

answered Feb 27 '15 at 05:50

Aakash

83
1
12

`if(...)`, `return(...)` works, but it's ugly by Python's standards i.e. [PEP 8](https://www.python.org/dev/peps/pep-0008/). `(ord(i)>=97) and (ord(i)<=122)` can be replaced with `97 <= ord(i) <=122`. – Cristian Ciupitu Feb 27 '15 at 19:28
Yes,you are totally correct...I guess it will take a while to drop my C coding style :) – Aakash Feb 27 '15 at 19:59

Encryption Python - encrypting a string

2 Answers2