CODEWITHSUNDEEP
pythonlistcaesar-cipher
Soham Karalkar
Soham Karalkar

Reputation: 43

How to match elements from input to list

I'm currently working on a Caesar cipher program, and I basically typed up a list of the alphabets: alphabet = ['a','b','c','d',...]

Then asked the user for a word to encrypt, text = input('Enter your message') and the shift amount, I figured I could set an empty string variable and then loop through (for loop) each letter to shift it.

But this is where I got stuck, how will I shift each letter in the input by the shift amount using the list?

I tried to loop through the input using the indexes of the list alphabet, but since had no idea what I was doing it didn't work.

Upvotes: 2

Views: 57

Answers (2)

Goku
Goku

Reputation: 1663

I'm not sure I fully understand what you are asking, but if you are just trying to shift by a constant amount to make a Cesar cipher, then this is fairly straightforward, you could have done with this a string rather than a list as well. The main thing to think about is the wrapping, which we can do with modulus operator. Lets say you want to shift 3 places: So if the index + shift is less than 26, the modulo operation doesn't change anything 2 + 3 % 26 = 5 If index + shift is 26 or greater, the modulo operation wraps it around. 24 + 3 % 26 = 1

example = "zebra"
alphabet = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

encrypted = ''
    
for char in example:
    if char in alphabet:
        i = alphabet.index(char)
        j = (i + 3) % 26
        encrypted += alphabet[j]
    else:
        encrypted += char

Upvotes: 0

Darshan A S
Darshan A S

Reputation: 381

Here's a generic implementation of the caesar-cipher, that should work for any shift amount, and any charset.

Feel free to get rid of the type hinting if you feel it hinders readability. I personally would prefer to have it though.

import string
from typing import Hashable, Iterable, Sequence, TypeVar

T = Hashable
def caesar_ciper(message: Iterable[T], k: int, charset: Sequence[T] = string.ascii_lowercase) -> Iterable[T]:
    n = len(charset)
    char_idx = dict(zip(charset, range(n)))
    shift = lambda x: charset[(char_idx[x] + k) % n]
    return map(shift, message)
    
message = 'abcxyz' # read from user
k = 3 # read from user

encoded = ''.join(caesar_ciper(message, k))
assert encoded == 'defabc'

Upvotes: 0

Related Questions