Caesar Cipher with key support.

Caesar Cipher.py

"""Substitution cypher, Ceasar's Cipher"""

from __future__ import print_function
import sys

MIN = 97
MAX = 122

def encode(text, n):
    """Encode the text.

    :text: the text to be encoded
    :n: the key, to rotate the text that number of time
    """
    encoded_text = ''
    for i in text.lower():
        if i.isalpha():
            encoded_char = ord(i)
            for i in range(n):
                if encoded_char == MAX:
                    encoded_char = MIN
                else:
                    encoded_char += 1
            encoded_text += chr(encoded_char)
        else:
            encoded_text += i
    return encoded_text

def decode(text, n):
    """Decode the text.

    :text: the text to be decoded
    :n: the key, to rotate the text that number of time
    """
    decoded_text = ''
    for i in text.lower():
        if i.isalpha():
            decoded_char = ord(i)
            for i in range(n):
                if decoded_char == MIN:
                    decoded_char = MAX
                else:
                    decoded_char -= 1
            decoded_text += chr(decoded_char)
        else:
            decoded_text += i
    return decoded_text

if __name__ == '__main__':
    get_input = input
    if sys.version_info[:2] <= (2, 7):
        get_input = raw_input
    while True:
        encode_or_decode = get_input('Enter "E" for encoding or "D" for decoding or "Q" for Quit: ').lower()
        if encode_or_decode == 'q':
            break
        if encode_or_decode not in ('e', 'd'):
            continue
        text = get_input('Enter text: ').lower()
        while not text:
            text = get_input('Please enter some text: ').lower()
        while True:
            key = get_input('Enter key (positive number): ')
            try:
                key = int(key)
            except ValueError:
                continue
            else:
                break
        if encode_or_decode == 'e':
            print(encode(text, key))
        elif encode_or_decode == 'd':
            print(decode(text, key))