url_shortener.py

from django.conf import settings


# Defining alphabet of custom base as [a-z] + [A-Z] + [0-9]
alphabet = map(chr, range(97, 123) + range(65, 91)) + map(str, range(0, 10))
base = len(alphabet)

def encode(str):
    reversed_str = str[::-1]
    pow_num = 0
    result = 0

    for i in range(0, len(reversed_str)):
        char = reversed_str[i]
        char_value = alphabet.index(char)
        result += char_value * pow(base, pow_num)
        pow_num += 1

    return result

def decode(i):
    result = ''
    
    if i < 0:
        raise ValueError('Must be a positive integer.')
    elif not i:
        result = alphabet[0]
    while i > 0:
        result = alphabet[i % base] + result
        i /= base

    return result

def get_url(short_url):
    return "http://%s/%s" % (settings.PROXY_DOMAIN, short_url)