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Re: save dictionary to a file without brackets.

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From Chris Kaynor <ckaynor@zindagigames.com>
Date Thu, 9 Aug 2012 14:51:17 -0700
Subject Re: save dictionary to a file without brackets.
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Xref csiph.com comp.lang.python:26821

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I realized, I should have done 10, 100, 1000 rather than 1, 10, 100
for better results, so here are the results for 1000 items. It still
maintains the same pattern:

>>> timeit.timeit('for i in d: pass', 'd=dict.fromkeys(range(1000))')
10.166595947685153
>>> timeit.timeit('for i in d.iteritems(): pass', 'd=dict.fromkeys(range(1000))')
19.922474218828711
>>> timeit.timeit('for i in d: v=d[i]', 'd=dict.fromkeys(range(1000))')
31.007666660415282

Chris

On Thu, Aug 9, 2012 at 2:49 PM, Chris Kaynor <ckaynor@zindagigames.com> wrote:
> On Thu, Aug 9, 2012 at 2:34 PM, Roman Vashkevich <vashkevichrb@gmail.com> wrote:
>>
>> Actually, they are different.
>> Put a dict.{iter}items() in an O(k^N) algorithm and make it a hundred thousand entries, and you will feel the difference.
>> Dict uses hashing to get a value from the dict and this is why it's O(1).
>>
>
> Using "in" as an operator such as: "if key in dict" or "result = key
> in dict" is O(1) as you say. Iterating on the dictionary requires
> touching every item, and so is O(n), even though it also using "in" in
> the command.
>
> Here are a few quick timing tests I just ran with Python 2.6:
>
>>>> timeit.timeit('for i in d: pass', 'd=dict.fromkeys(range(1))')
> 0.078683853332734088
>>>> timeit.timeit('for i in d: pass', 'd=dict.fromkeys(range(10))')
> 0.17451784110969015
>>>> timeit.timeit('for i in d: pass', 'd=dict.fromkeys(range(100))')
> 1.1708168159579486
>
>>>> timeit.timeit('for i in d.iteritems(): pass', 'd=dict.fromkeys(range(1))')
> 0.14186911440299355
>>>> timeit.timeit('for i in d.iteritems(): pass', 'd=dict.fromkeys(range(10))')
> 0.33836512561802579
>>>> timeit.timeit('for i in d.iteritems(): pass', 'd=dict.fromkeys(range(100))')
> 2.2544262854249268
>
>>>> timeit.timeit('for i in d: v=d[i]', 'd=dict.fromkeys(range(1))')
> 0.10009793211446549
>>>> timeit.timeit('for i in d: v=d[i]', 'd=dict.fromkeys(range(10))')
> 0.38825072496723578
>>>> timeit.timeit('for i in d: v=d[i]', 'd=dict.fromkeys(range(100))')
> 3.3020098061049339
>
>
> As can be seen here, a 1-item dictionary iterated in 0.07 seconds, 10
> items in 0.17 seconds, and 100 items in 1.17 seconds. That is fairly
> close to linear, especially when considering the overhead of a
> complete no-op
>
> Using iteritems, it appears to actually scale slightly better than
> linear, though it is slower than just the plain iteration.
>
> Doing a plain iteration, then looking up the keys to get the values
> also appears to be linear, and is even slower than iteritems.

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save dictionary to a file without brackets. giuseppe.amatulli@gmail.com - 2012-08-09 13:11 -0700
  Re: save dictionary to a file without brackets. Roman Vashkevich <vashkevichrb@gmail.com> - 2012-08-10 00:22 +0400
  Re: save dictionary to a file without brackets. Tim Chase <python.list@tim.thechases.com> - 2012-08-09 15:35 -0500
  Re: save dictionary to a file without brackets. Giuseppe Amatulli <giuseppe.amatulli@gmail.com> - 2012-08-09 15:35 -0500
  Re: save dictionary to a file without brackets. Gelonida N <gelonida@gmail.com> - 2012-08-09 22:35 +0200
  Re: save dictionary to a file without brackets. Giuseppe Amatulli <giuseppe.amatulli@gmail.com> - 2012-08-09 15:38 -0500
  Re: save dictionary to a file without brackets. Roman Vashkevich <vashkevichrb@gmail.com> - 2012-08-10 00:41 +0400
  Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-09 22:17 +0100
  Re: save dictionary to a file without brackets. Tim Chase <python.list@tim.thechases.com> - 2012-08-09 16:21 -0500
  Re: save dictionary to a file without brackets. Roman Vashkevich <vashkevichrb@gmail.com> - 2012-08-10 01:34 +0400
    Re: save dictionary to a file without brackets. Andrew Cooper <amc96@cam.ac.uk> - 2012-08-09 23:03 +0100
      Re: save dictionary to a file without brackets. Dave Angel <d@davea.name> - 2012-08-09 18:26 -0400
        Re: save dictionary to a file without brackets. Andrew Cooper <amc96@cam.ac.uk> - 2012-08-09 23:54 +0100
          Re: save dictionary to a file without brackets. Roy Smith <roy@panix.com> - 2012-08-09 19:05 -0400
            Re: save dictionary to a file without brackets. Chris Angelico <rosuav@gmail.com> - 2012-08-10 09:14 +1000
              Re: save dictionary to a file without brackets. Roy Smith <roy@panix.com> - 2012-08-09 19:24 -0400
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-10 00:33 +0100
                Re: save dictionary to a file without brackets. Tim Chase <python.list@tim.thechases.com> - 2012-08-09 19:16 -0500
                Re: save dictionary to a file without brackets. Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-10 08:54 +0000
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-10 10:37 +0100
                Re: save dictionary to a file without brackets. Roy Smith <roy@panix.com> - 2012-08-10 08:29 -0400
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-10 15:47 +0100
                Re: save dictionary to a file without brackets. alex23 <wuwei23@gmail.com> - 2012-08-12 17:15 -0700
                Re: save dictionary to a file without brackets. Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-13 08:05 +0000
                Re: save dictionary to a file without brackets. alex23 <wuwei23@gmail.com> - 2012-08-13 09:16 -0700
                Re: save dictionary to a file without brackets. rusi <rustompmody@gmail.com> - 2012-08-13 08:55 -0700
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-13 13:37 +0100
                Re: save dictionary to a file without brackets. alex23 <wuwei23@gmail.com> - 2012-08-13 09:14 -0700
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-13 18:07 +0100
                Re: save dictionary to a file without brackets. Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-14 02:54 +0000
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-14 12:33 +0100
                Re: save dictionary to a file without brackets. Alister <alister.ware@ntlworld.com> - 2012-08-14 15:05 +0000
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-14 19:15 +0100
                Re: save dictionary to a file without brackets. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-13 18:43 +0100
                Re: save dictionary to a file without brackets. alex23 <wuwei23@gmail.com> - 2012-08-13 18:32 -0700
                Re: save dictionary to a file without brackets. Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-08-10 12:34 -0400
                Re: save dictionary to a file without brackets. Dave Angel <d@davea.name> - 2012-08-09 20:27 -0400
                Re: save dictionary to a file without brackets. Chris Angelico <rosuav@gmail.com> - 2012-08-10 10:31 +1000
          Re: save dictionary to a file without brackets. Dave Angel <d@davea.name> - 2012-08-09 19:38 -0400
      Re: save dictionary to a file without brackets. Tim Chase <python.list@tim.thechases.com> - 2012-08-09 17:39 -0500
      Re: save dictionary to a file without brackets. Chris Kaynor <ckaynor@zindagigames.com> - 2012-08-09 15:37 -0700
      Re: save dictionary to a file without brackets. Chris Angelico <rosuav@gmail.com> - 2012-08-10 08:53 +1000
        Re: save dictionary to a file without brackets. Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-11 11:26 +0000
          Re: save dictionary to a file without brackets. 88888 Dihedral <dihedral88888@googlemail.com> - 2012-08-12 04:59 -0700
      Re: save dictionary to a file without brackets. Chris Angelico <rosuav@gmail.com> - 2012-08-10 09:01 +1000
      Re: save dictionary to a file without brackets. Dave Angel <d@davea.name> - 2012-08-09 19:42 -0400
      Re: save dictionary to a file without brackets. 88888 Dihedral <dihedral88888@googlemail.com> - 2012-08-09 22:35 -0700
  Re: save dictionary to a file without brackets. Terry Reedy <tjreedy@udel.edu> - 2012-08-09 17:46 -0400
  Re: save dictionary to a file without brackets. Dave Angel <d@davea.name> - 2012-08-09 17:47 -0400
    Re: save dictionary to a file without brackets. 88888 Dihedral <dihedral88888@googlemail.com> - 2012-08-10 10:46 -0700
    Re: save dictionary to a file without brackets. 88888 Dihedral <dihedral88888@googlemail.com> - 2012-08-10 10:46 -0700
  Re: save dictionary to a file without brackets. Chris Kaynor <ckaynor@zindagigames.com> - 2012-08-09 14:49 -0700
  Re: save dictionary to a file without brackets. Chris Kaynor <ckaynor@zindagigames.com> - 2012-08-09 14:51 -0700
  Re: save dictionary to a file without brackets. Giuseppe Amatulli <giuseppe.amatulli@gmail.com> - 2012-08-09 16:53 -0500
  Re: save dictionary to a file without brackets. Roman Vashkevich <vashkevichrb@gmail.com> - 2012-08-10 02:02 +0400

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