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Re: Generate unique ID for URL

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I found the MD5 and SHA hashes slow to calculate.
The builtin hash is fast but I was concerned about collisions. What
rate of collisions could I expect?

Outside attacks not an issue and multiple processes would be used.


On Wed, Nov 14, 2012 at 11:26 AM, Chris Kaynor <ckaynor@zindagigames.com> wrote:
> One option would be using a hash. Python's built-in hash, a 32-bit
> CRC, 128-bit MD5, 256-bit SHA or one of the many others that exist,
> depending on the needs. Higher bit counts will reduce the odds of
> accidental collisions; cryptographically secure ones if outside
> attacks matter. In such a case, you'd have to roll your own means of
> converting the hash back into the string if you ever need it for
> debugging, and there is always the possibility of collisions. A
> similar solution would be using a pseudo-random GUID using the url as
> the seed.
>
> You could use a counter if all IDs are generated by a single process
> (and even in other cases with some work).
>
> If you want to be able to go both ways, using base64 encoding is
> probably your best bet, though you might get benefits by using
> compression.
> Chris
>
>
> On Tue, Nov 13, 2012 at 3:56 PM, Richard <richardbp@gmail.com> wrote:
>> Good point - one way encoding would be fine.
>>
>> Also this is performed millions of times so ideally efficient.
>>
>>
>> On Wednesday, November 14, 2012 10:34:03 AM UTC+11, John Gordon wrote:
>>> In <0692e6a2-343c-4eb0-be57-fe5c815efb99@googlegroups.com> Richard <richardbp@gmail.com> writes:
>>>
>>>
>>>
>>> > I want to create a URL-safe unique ID for URL's.
>>>
>>> > Currently I use:
>>>
>>> > url_id = base64.urlsafe_b64encode(url)
>>>
>>>
>>>
>>> > >>> base64.urlsafe_b64encode('docs.python.org/library/uuid.html')
>>>
>>> > 'ZG9jcy5weXRob24ub3JnL2xpYnJhcnkvdXVpZC5odG1s'
>>>
>>>
>>>
>>> > I would prefer more concise ID's.
>>>
>>> > What do you recommend? - Compression?
>>>
>>>
>>>
>>> Does the ID need to contain all the information necessary to recreate the
>>>
>>> original URL?
>>>
>>>
>>>
>>> --
>>>
>>> John Gordon                   A is for Amy, who fell down the stairs
>>>
>>> gordon@panix.com              B is for Basil, assaulted by bears
>>>
>>>                                 -- Edward Gorey, "The Gashlycrumb Tinies"
>>
>> --
>> http://mail.python.org/mailman/listinfo/python-list

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Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 15:20 -0800
  Re: Generate unique ID for URL John Gordon <gordon@panix.com> - 2012-11-13 23:34 +0000
    Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 15:56 -0800
      Re: Generate unique ID for URL Chris Kaynor <ckaynor@zindagigames.com> - 2012-11-13 16:26 -0800
      Re: Generate unique ID for URL Richard Baron Penman <richardbp@gmail.com> - 2012-11-14 11:41 +1100
        Re: Generate unique ID for URL Johannes Bauer <dfnsonfsduifb@gmx.de> - 2012-11-14 10:44 +0100
          Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-14 03:14 -0800
      Re: Generate unique ID for URL Christian Heimes <christian@python.org> - 2012-11-14 01:43 +0100
        Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 16:50 -0800
          Re: Generate unique ID for URL Christian Heimes <christian@python.org> - 2012-11-14 02:05 +0100
      Re: Generate unique ID for URL Christian Heimes <christian@python.org> - 2012-11-14 01:59 +0100
        Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 17:18 -0800
        Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 17:18 -0800
  Re: Generate unique ID for URL Miki Tebeka <miki.tebeka@gmail.com> - 2012-11-13 16:13 -0800
    Re: Generate unique ID for URL Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-14 02:04 +0000
      Re: Generate unique ID for URL Steve Howell <showell30@yahoo.com> - 2012-11-13 18:32 -0800
        Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 19:12 -0800
  Re: Generate unique ID for URL Roy Smith <roy@panix.com> - 2012-11-13 20:39 -0500
    Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 19:25 -0800
      Re: Generate unique ID for URL Roy Smith <roy@panix.com> - 2012-11-13 22:38 -0500
        Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 19:56 -0800
      Re: Generate unique ID for URL Chris Angelico <rosuav@gmail.com> - 2012-11-14 15:06 +1100
        Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 20:14 -0800
        Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 20:14 -0800
    Re: Generate unique ID for URL Richard <richardbp@gmail.com> - 2012-11-13 19:27 -0800
    Re: Generate unique ID for URL Johannes Bauer <dfnsonfsduifb@gmx.de> - 2012-11-14 12:29 +0100
      Re: Generate unique ID for URL Dave Angel <d@davea.name> - 2012-11-14 07:33 -0500
        Re: Generate unique ID for URL Johannes Bauer <dfnsonfsduifb@gmx.de> - 2012-11-14 14:00 +0100

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