Question

I am working in python on appengine.

I am trying to create what is equivalent to the “v” value in the youtube url’s (http://www.youtube.com/watch?v=XhMN0wlITLk) for retrieving specific entities. The datastore auto generates a key but it is way too long (34 digits). I have experimented with hashlib to build my own, but again I get a long string. I would like to keep it to under 11 digits (I am not dealing with a huge number of entities) and letters and numbers are acceptable.

It seems like there should be a pretty standard solution. I am probably just missing it.

Answer 1

You can use the auto generated integer id of the key to generate the hash. A simple way to generate the hash would be to convert the integer id to base62 (alphanumeric). To fetch the object simply convert to decimal back from base62 and use get_by_id to retrieve the object.

Here is a simple base62 conversion function that i have used in one of my apps.

import string
alphabet = string.letters + string.digits
max = 11

def int_to_base62(num):
    if num == 0:
        return alphabet[0]

    arr = []
    radix = len(alphabet)
    while num:
        arr.append(alphabet[num%radix])
        num /= radix
    arr.reverse()
    return (alphabet[0] * (max - len(arr))) + ''.join(arr)

def base62_to_int(str):
    radix = len(alphabet)
    power = len(str) - 1
    num = 0
    for char in str:
        num += alphabet.index(char) * (radix ** power)
        power -= 1
    return num