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Re: hashing strings to integers

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On 2014-05-27, Steven D'Aprano wrote:

> On Tue, 27 May 2014 16:13:46 +0100, Adam Funk wrote:

>> Well, here's the way it works in my mind:
>> 
>>    I can store a set of a zillion strings (or a dict with a zillion
>>    string keys), but every time I test "if new_string in seen_strings",
>>    the computer hashes the new_string using some kind of "short hash",
>>    checks the set for matching buckets (I'm assuming this is how python
>>    tests set membership --- is that right?), 
>
> So far so good. That applies to all objects, not just strings.
>
>
>>    then checks any
>>    hash-matches for string equality.  Testing string equality is slower
>>    than integer equality, and strings (unless they are really short)
>>    take up a lot more memory than long integers.
>
> But presumably you have to keep the string around anyway. It's going to 
> be somewhere, you can't just throw the string away and garbage collect 
> it. The dict doesn't store a copy of the string, it stores a reference to 
> it, and extra references don't cost much.

In the case where I did something like that, I wasn't keeping copies
of the strings in memory after hashing (& otherwise processing them).
I know that putting the strings' pointers in the set is a light memory
load.



[snipping the rest because...]

You've convinced me.  Thanks.



-- 
I heard that Hans Christian Andersen lifted the title for "The Little
Mermaid" off a Red Lobster Menu.                         [Bucky Katt]

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Thread

hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 12:47 +0100
  Re: hashing strings to integers for sqlite3 keys Peter Otten <__peter__@web.de> - 2014-05-22 14:58 +0200
    Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 14:41 +0100
      Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-23 00:08 +1000
        Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 15:40 +0100
  Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-22 23:03 +1000
    Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 14:47 +0100
  Re: hashing strings to integers for sqlite3 keys Tim Chase <python.list@tim.thechases.com> - 2014-05-22 08:09 -0500
    Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 14:54 +0100
      Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-23 00:14 +1000
        Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 15:47 +0100
          Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-23 01:09 +1000
          Re: hashing strings to integers for sqlite3 keys Peter Otten <__peter__@web.de> - 2014-05-22 17:34 +0200
            hashing strings to integers (was: hashing strings to integers for sqlite3 keys) Adam Funk <a24061@ducksburg.com> - 2014-05-23 11:27 +0100
              Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-05-23 11:36 +0100
                Re: hashing strings to integers Chris Angelico <rosuav@gmail.com> - 2014-05-23 21:01 +1000
              Re: hashing strings to integers (was: hashing strings to integers for sqlite3 keys) Chris Angelico <rosuav@gmail.com> - 2014-05-23 20:59 +1000
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-05-27 16:13 +0100
                Re: hashing strings to integers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-27 17:02 +0000
                Re: hashing strings to integers Chris Angelico <rosuav@gmail.com> - 2014-05-28 05:16 +1000
                Re: hashing strings to integers Dan Sommers <dan@tombstonezero.net> - 2014-05-28 01:55 +0000
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-06-03 11:29 +0100
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-06-03 11:32 +0100
              Re: hashing strings to integers Terry Reedy <tjreedy@udel.edu> - 2014-05-23 15:10 -0400
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-05-27 16:20 +0100
  Re: hashing strings to integers for sqlite3 keys alister <alister.nospam.ware@ntlworld.com> - 2014-05-22 14:48 +0000

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