Here is a good talk on how dictionaries are implemented in python : http://blip.tv/pycon-us-videos-2009-2010-2011/pycon-2010-the-mighty-dictionary-55-3352147
Due to possibility of collisions in the hash table, dict keeps allocating 4x or 2x the size of existing allocation and *will* reorder the items when such an operation happens. They go and acquire more memory when the dict is 2/3rds full. But the reverse is not possible. A dummy key has to be inserted in a free slot, so that valid items in the dictionary can be found. Since all this depends on the order of insertion, you cannot guarantee that copying existing items into a new dictionary will consume less space. If look up times is not a concern, and you are trying to optimize for space the stackoverflow link that Anand shared earlier could help. Regards, Harish On Thu, Apr 18, 2013 at 12:06 PM, Hrishikesh Kulkarni <ri...@turtleyogi.com>wrote: > On Wed, Apr 17, 2013 at 9:30 PM, Rahul R <rahul8...@gmail.com> wrote: > > > As far as i know, python performs a lazy deletion of values , when we > > delete content from a dictionary (correct me if i am wrong) . So, when > we > > insert a lot of values the dictionary automatically expands. I don't see > > dict shrinking when we delete values from dictionary. In such case, is > > there a way to forcibly reduce the dictionary size ? > > > > > Are you measuring this shrinking? > the following in dictobject.c should guide you with the internals. The > deleted item is simply replaced with a refcounted dummy. The deleted item > is marked for cleanup by gc with decref. > > PyDict_DelItem () : > .. > old_key = ep->me_key; > Py_INCREF(dummy); > ep->me_key = dummy; > old_value = ep->me_value; > ep->me_value = NULL; > mp->ma_used--; > Py_DECREF(old_value); > Py_DECREF(old_key); > .. > > > dict_length(): > .. > return mp->ma_used; > .. > > PyDict_Size(): > .. > return ((PyDictObject *)mp)->ma_used; > .. > > > > regards, > Rishi > > > > > > > > ./Rahul > > > > On Wed, Apr 17, 2013 at 9:23 PM, Ramdas S <ram...@gmail.com> wrote: > > > > > On Wed, Apr 17, 2013 at 9:22 PM, Rahul R <rahul8...@gmail.com> wrote: > > > > > > > Ahh , sorry If i wasnt clear the first time. I dint mean reorder the > > data > > > > in dictionary. I meant resize the dictionary. > > > > > > > > > > What do you mean by resize? > > > > > > > > > > > > > > ./Rahul > > > > > > > > On Wed, Apr 17, 2013 at 9:05 PM, Anand Chitipothu < > > anandol...@gmail.com > > > > >wrote: > > > > > > > > > dictionaries are unordered. It is not a good idea to expect any > order > > > in > > > > > dictionaries, even if you are seeing some order by chance. > > > > > > > > > > If you need order, then use OrderedDict from collections module > (new > > in > > > > > Python 2.7). > > > > > > > > > > Anand > > > > > > > > > > > > > > > On Wed, Apr 17, 2013 at 9:00 PM, Rahul R <rahul8...@gmail.com> > > wrote: > > > > > > > > > > > Hey Guys, > > > > > > > > > > > > Is it possible to forcibly reorder the python dictionary after > "n" > > > > number > > > > > > of inserts and deletions. As far as i know, python dictionary > > > performs > > > > > lazy > > > > > > deletes. Thus , even if the data is deleted, python has a dummy > > data > > > > > their > > > > > > in order to preserve consistency. The python dictionary > > > > > > keeps expanding when the size of dict is increasing, but after > > > > deleting a > > > > > > few parameters the size does not decrease. Is there a way , > where I > > > can > > > > > > forcibly resize the dictionary ? > > > > > > > > > > > > I was thinking of copying content from existing dictionary to new > > > dict > > > > > and > > > > > > deleting the previous one.But thats a cumbersome operation. > > > > > > > > > > > > Thanks, > > > > > > ./Rahul > > > > > > _______________________________________________ > > > > > > BangPypers mailing list > > > > > > BangPypers@python.org > > > > > > http://mail.python.org/mailman/listinfo/bangpypers > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > Anand > > > > > http://anandology.com/ > > > > > _______________________________________________ > > > > > BangPypers mailing list > > > > > BangPypers@python.org > > > > > http://mail.python.org/mailman/listinfo/bangpypers > > > > > > > > > _______________________________________________ > > > > BangPypers mailing list > > > > BangPypers@python.org > > > > http://mail.python.org/mailman/listinfo/bangpypers > > > > > > > > > > > > > > > > -- > > > Ramdas S > > > +91 9342 583 065 > > > My Personal Blog on http://ramdaz.wordpress.com > > > _______________________________________________ > > > BangPypers mailing list > > > BangPypers@python.org > > > http://mail.python.org/mailman/listinfo/bangpypers > > > > > _______________________________________________ > > BangPypers mailing list > > BangPypers@python.org > > http://mail.python.org/mailman/listinfo/bangpypers > > > _______________________________________________ > BangPypers mailing list > BangPypers@python.org > http://mail.python.org/mailman/listinfo/bangpypers > _______________________________________________ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
