cs-l25.py

import string

class CyclicList(list):
    def __getitem__(self, x):
        index = x.__index__()
        return super().__getitem__(index % len(self))

l = CyclicList(string.ascii_lowercase+string.punctuation+string.whitespace)

inp = input("Enter text: ").lower()

if not all(char for char in inp if char in l):
    raise TypeError("Not all letters")

shift = int(input("Enter amount to shift by: "))

print("".join(map(lambda char: l[l.index(char)+shift], inp)))