A Python function to perform rot13 encoding

rot13.py

from this import s


# Without long strings
def rot13(x):
    abc = "".join(map(chr, range(65, 91)))
    a_to_m = x in abc[:13] + abc[:13].lower()
    n_to_z = x in abc[13:] + abc[13:].lower()
    return chr(ord(x) + 13 * (a_to_m or -n_to_z))


# With long strings
def rot13(x):
    a_to_m = x in "abcdefghijklmABCDEFGHIJKLM"
    n_to_z = x in "nopqrstuvwxyzNOPQRSTUVWXYZ"
    return chr(ord(x) + 13 * (a_to_m or -n_to_z))


# With a dictionary comprehension
def rot13(x):
    return {chr(i + c): chr((i + 13) % 26 + c) for i in range(26) for c in (65, 97)}.get(x, x)


# My second favorite
def rot13(x):
    if x.isalpha():
        start = 65 if x.isupper() else 97
        shift = (ord(x) - start + 13) % 26
        return chr(start + shift)
    return x


# My favorite
def rot13(x):
    if x.isalpha():
        shift = 13 if "a" <= x.lower() <= "m" else -13
        return chr(ord(x) + shift)
    return x


# No variables
def rot13(x):
    if x.isalpha():
        return chr(ord(x) + (13 if "a" <= x.lower() <= "m" else -13))
    return x


# All on one line
def rot13(x):
    return chr(ord(x) + (13 if "a" <= x.lower() <= "m" else -13)) if x.isalpha() else x


"".join(map(rot13, s))