Simple base converter for Py

encoder.py

#!/usr/bin/env python3

ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

def encode(n):
    result = ""
    while (n > 0):
        n,m = divmod(n,len(ALPHABET))
        result = ALPHABET[m] + result
    return result

def decode(encoded):
    result = 0
    for i in range(len(encoded)):
        value = ALPHABET.index(encoded[i])
        result += value * (len(ALPHABET) ** (len(encoded) - i - 1))
    return result

n = 4503599627371331

print("IN:  %d" % n)
enc = encode(n)
print("ENC: %s" % enc)
dec = decode(enc)
print("OUT: %d" % dec)

Adapted slightly from http://jeffreypratt.net/safely-base-36-encoding-integers.html