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From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: stable object serialization to text file
Date: Thu, 12 Jan 2012 15:15:54 -0500
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On 1/12/2012 7:24 AM, Peter Otten wrote:
> M=C3=A1t=C3=A9 Koch wrote:
>
>> I'm developing an app which stores the data in file system database. T=
he
>> data in my case consists of large python objects, mostly dicts, contai=
ning
>> texts and numbers. The easiest way to dump and load them would be pick=
le,
>> but I have a problem with it: I want to keep the data in version contr=
ol,
>> and I would like to use it as efficiently as possible. Is it possible =
to
>> force pickle to store the otherwise unordered (e.g. dictionary) data i=
n a
>> kind of ordered way, so that if I dump a large dict, then change 1 tin=
y
>> thing in it and dump again, the diff of the former and the new file wi=
ll
>> be minimal?
>>
>> If pickle is not the best choice for me, can you suggest anything else=
?
>> (If there isn't any solution for it so far, I will write the module of=

>> course, but first I'd like to look around and make sure it hasn't been=

>> created yet.)
>
> Have you considered json?
>
> http://docs.python.org/library/json.html
>
> The encoder features a sort_keys flag which might help.

If that does not do it for you, consider that a dict is a two-column=20
table, with arbitrary structures in each column. Convert to list with=20
sorted(somedict.items()). This is basically what json should do. Then=20
write to a text stream, one line per key,value pair. Whether you put the =

text into an os file in a directory (a hierachical database ;-) or a=20
text field in another database is up to you. Either way, diffs are easy.

--=20
Terry Jan Reedy