Caesar Cipher in Python

CaesarCipher.py

import string


def gen_dic(key):
    cap_map = {}
    small_map = {}
    cap_shift = list(string.ascii_uppercase)
    small_shift = list(string.ascii_lowercase)
    cap_append = cap_shift[:key]
    small_append = small_shift[:key]
    cap_shift = cap_shift[key:]
    small_shift = small_shift[key:]
    cap_shift += cap_append
    small_shift += small_append
    for c, e in zip(list(string.ascii_uppercase), cap_shift):
        cap_map[c] = e
    for c, e in zip(list(string.ascii_lowercase), small_shift):
        small_map[c] = e
    return cap_map, small_map


def encrypt(key, s):
    key = int(key)
    s = list(s)
    caps, smalls = gen_dic(key)
    for i in range(len(s)):
        capital_alpha = s[i] in list(string.ascii_uppercase)
        small_alpha = s[i] in list(string.ascii_lowercase)
        if capital_alpha:
            s[i] = caps[s[i]]
        elif small_alpha:
            s[i] = smalls[s[i]]
    return ''.join(s)


def decrypt(key, s):
    key = int(key)
    s = list(s)
    caps, smalls = gen_dic(key)
    caps = dict([(value, key) for key, value in caps.items()])
    smalls = dict([(value, key) for key, value in smalls.items()])
    for i in range(len(s)):
        capital_alpha = s[i] in list(string.ascii_uppercase)
        small_alpha = s[i] in list(string.ascii_lowercase)
        if capital_alpha:
            s[i] = caps[s[i]]
        elif small_alpha:
            s[i] = smalls[s[i]]
    return ''.join(s)