Re: Generating a unique identifier

On Fri, 07 Sep 2007 08:47:58 -0700, Paul Rubin wrote:

Paul Rubin <http://phr.cx@xxxxxxxxxxxxxx> writes:
def unique_id():
return os.urandom(10).encode('hex')

Sorry, make that 32 or 40 instead of 10, if the number of id's is large,
to make birthday collisions unlikely.

I did a small empirical test, and with 16 million ids, I found no
collisions.

However, I did find that trying to dispose of a set of 16 million short
strings caused my Python session to lock up for twenty minutes until I
got fed up and killed the process. Should garbage-collecting 16 million
strings really take 20+ minutes?


If you don't want the id's to be that large, you can implement a Feistel
cipher using md5 or sha as the round function pretty straightforwardly,
then just feed successive integers through it. That also guarantees
uniqueness, at least within one run of the program. I have some sample
code around for that, let me know if you need it.

I'm not sure that I need it, but I would certainly be curious to see it.


Thanks,


--
Steven.
.

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