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Newsgroups: comp.lang.python
Date: Sat, 29 Sep 2012 06:35:02 -0700 (PDT)
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Subject: Re: [python-list] python application file format
From: Ramchandra Apte <maniandram01@gmail.com>
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On Saturday, 29 September 2012 02:05:07 UTC+5:30, Prasad, Ramit  wrote:
> Benjamin Jessup wrote:
> 
> > Hello all,
> 
> > 
> 
> > What do people recommend for a file format for a python desktop
> 
> > application? Data is complex with 100s/1000s of class instances, which
> 
> > reference each other.
> 
> > 
> 
> > Write the file with struct module? (Rebuild object pointers, safe,
> 
> > compact, portable, not expandable without reserved space)
> 
> > 
> 
> > Use cPickle with a module/class whitelist? (Can't easily port, not
> 
> > entirely safe, compact enough, expandable)
> 
> > 
> 
> > Use JSON or similar? (Rebuild object pointers, portable, expandable, size?)
> 
> > 
> 
> > Any advice is greatly appreciated!
> 
> 
> 
> I would think your options are pickle, json or database (either sqlite or 
> 
> something like Postgres). I am unfamiliar with the struct module so I 
> 
> cannot comment on its applicability.
> 
> 
> 
> I would guess that your data would be best saved by using a sqlite 
> 
> database. Your biggest problem might be how the different classes are 
> 
> referencing each other. If you are using identifiers then any of these 
> 
> options will probably work. If you are using aggregation then I know
> 
> that pickle will work (at least for built-in types). JSON will
> 
> keep the structure but duplicate elements.
> 
> 
> 
> 
> 
> >>> a = [ 1,2,3 ]
> 
> >>> b = [ 'a', 'b', 'c' ]
> 
> >>> a.append( b )
> 
> >>> e = [ a,b ]
> 
> >>> s = json.dumps( e ) 
> 
> >>> eret = json.loads( s )
> 
> >>> id(eret[0][3]), id(eret[1]) # Same result for json and simplejson
> 
> (329443808, 327677272) 
> 
> >>> eret[0][3].append( 'o')
> 
> >>> eret[0][3], eret[1]
> 
> ([u'a', u'b', u'c', 'o'], [u'a', u'b', u'c'])
> 
> 
> 
> So pickle will be your easiest option, but I am not sure how well it
> 
> will scale with a large number items. Using sqlite/db should scale well
> 
> but it will take you longer/more effort to create a system for converting 
> 
> your objects to and from the DB.
> 
> 
> 
> 
> 
> 
> 
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Guess I shouldn't read or rely your posts (virus'es could be in them) :-D