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Groups > comp.lang.python > #26827
| References | (3 earlier) <36EA3847-6713-4C12-B47B-9B5E10325F00@gmail.com> <502429C3.5000600@tim.thechases.com> <mailman.3120.1344548050.4697.python-list@python.org> <MsWUr.1183213$%k.489563@fx20.am4> <5024392D.3010306@davea.name> |
|---|---|
| From | Chris Kaynor <ckaynor@zindagigames.com> |
| Date | 2012-08-09 15:37 -0700 |
| Subject | Re: save dictionary to a file without brackets. |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.3131.1344551903.4697.python-list@python.org> (permalink) |
On Thu, Aug 9, 2012 at 3:26 PM, Dave Angel <d@davea.name> wrote:
> On 08/09/2012 06:03 PM, Andrew Cooper wrote:
>> On 09/08/2012 22:34, Roman Vashkevich 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).
>>>
>> Sligtly off topic, but looking up a value in a dictionary is actually
>> O(n) for all other entries in the dict which suffer a hash collision
>> with the searched entry.
>>
>> True, a sensible choice of hash function will reduce n to 1 in common
>> cases, but it becomes an important consideration for larger datasets.
>>
>> ~Andrew
>
> I'm glad you're wrong for CPython's dictionaries. The only time the
> lookup would degenerate to O[n] would be if the hash table had only one
> slot. CPython sensibly increases the hash table size when it becomes
> too small for efficiency.
>
>
> Where have you seen dictionaries so poorly implemented?
There are plenty of ways to make a pathological hash function that
will have that issue in CPython.
The very simple (and stupid):
class O(object):
def __hash__(self):
return 0
def __eq__(self, other): # I am aware this is the default equals method.
return self is other
Start adding those to a dictionary to get O(n) lookups.
Any case the hash return values modulus the dictionary hash table size
is constant will have similar results; powers of 2 are likely to
result in such behavior as well.
>
> --
>
> DaveA
>
> --
> http://mail.python.org/mailman/listinfo/python-list
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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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