Python3

alphabet = "abcdefghijklmnopqrstuvwxyz"
alphabet_cap = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
encrypted = ""

#calculate new k if k is greater than 26
if k > 26:
    k = k % 26

#rotate alphabet by k
rotated_alphabet = alphabet[k:] + alphabet[:k]
rotated_alphabet_cap = alphabet_cap[k:] + alphabet_cap[:k]


#encrypt
for i in range(len(s)):

    #uppercase letters
    if s[i].isupper():
        index = alphabet_cap.index(s[i])
        encrypted += rotated_alphabet_cap[index]

    #lowercase letters
    elif s[i].islower():
        index = alphabet.index(s[i])
        encrypted += rotated_alphabet[index]

    #punctuation, hyphens, etc
    else:
        encrypted += s[i]

return encrypted