cPickle

[Maric Michaud]

Le Thursday 04 September 2008 13:08:59 Gerhard Häring, vous avez écrit :
> gopal mishra wrote:
> > I have 3 objects and want to save in one pickle file.
> >
> > I used cPickle to dump 3 objects in a pkl file
> >
> > i.e  cPickle.dump(object1, fileobject,  -1)
> >
> >                  cPickle.dump(object2, fileobject,  -1)
> >
> >                  cPickle.dump(object3, fileobject,  -1)
> >
> >
> >
> > I have changed the 3^rd object and  want to save the updated 3^rd object
> > in the pickle file.
> >
> > I have to dump all the 3 objects again.
> >
> > Is there any way to dump only the 3^rd object in to the pkl file.
>
> No, there isn't. You could, of course, save each object in its own
> pickle file. Or use an object database like ZODB instead.
>

Shelve is another alternative, shipped with python and rather straightforward. 
Shelve as ZODB use pickles of objects but, unlike ZODB, won't need you change 
anything  to your actual classes.

>>>[8]: import shelve

>>>[9]: s = shelve.open('db')

>>>[10]: a, b, c = 5, 4., ("foo", "bar")

>>>[11]: s['a'], s['b'], s['c'] = a, b, c

>>>[12]: s.close()

>>>[13]:
maric at redflag1 13:46:42:~$ file db
db: Berkeley DB (Hash, version 8, native byte-order)
maric at redflag1 13:46:44:~$ ipython

>>>[1]: import shelve

>>>[2]: s = shelve.open('db')

>>>[3]: for name, value in s.items() : print name, value
   ...:
b 4.0
a 5
c ('foo', 'bar')

>>>[5]: del s['b']

>>>[6]: s['c'] += ('baz',)

>>>[7]: s.sync()

>>>[8]:
maric at redflag1 13:48:12:~$ ipython

>>>[1]: import shelve

>>>[2]: s = shelve.open('db')

>>>[3]: for name, value in s.items() : print name, value
   ...:
a 5
c ('foo', 'bar', 'baz')

The sync method may not work on all platform, maybe you'll have to close and 
re-open the db file to write to disk.

-- 
_____________

Maric Michaud