Encode and decode letters and numbers using ROT13 and ROT5

rot.py

#!/usr/bin/env python

# ROT: encode and decode letters and numbers using ROT13 and ROT5
# Author: Andrea Stagi <stagi.andrea@gmail.com>
# License: c'mon default header, don't be silly :D

def rot_encode(clr_str):

    rot_chars = []

    for ch in clr_str:
        ch_dec = ord(ch)
        if 65 <= ch_dec <= 90:
            rot_chars.append(chr((ch_dec + 13) % 65 % 26 + 65))
        elif 97 <= ch_dec <= 122:
            rot_chars.append(chr((ch_dec + 13) % 97 % 26 + 97))
        elif 48 <= ch_dec <= 57:
            rot_chars.append(chr((ch_dec + 5) % 48 % 10 + 48))
        else:
            rot_chars.append(ch)

    return ''.join(rot_chars)

def rot_decode(enc_str):

    rot_chars = []

    for ch in enc_str:
        ch_dec = ord(ch)
        if 65 <= ch_dec <= 90:
            rot_chars.append(chr((ch_dec % 65 - 13) % 26 + 65))
        elif 97 <= ch_dec <= 122:
            rot_chars.append(chr((ch_dec % 97 - 13) % 26 + 97))
        elif 48 <= ch_dec <= 57:
            rot_chars.append(chr((ch_dec % 48 - 5) % 10 + 48))
        else:
            rot_chars.append(ch)

    return ''.join(rot_chars)

morning_str = "Good morning Mr. Andrea! How are you? Today is 28th of May!"
print "Initial string: '%s'" % morning_str
enc_str = rot_encode(morning_str)
print "Encoded string: '%s'" % enc_str
dec_str = rot_decode(enc_str)
print "Decoded string: '%s'" % dec_str