cPickle error when caching data
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From: Benedict Verheyen on 3 Aug 2010 09:16 Hi i get the following error when trying to set data in the cache of a django application. The error is however a python error as it involves pickling and i can reproduce it in a shell. The error i get is this: cPickle.PicklingError: Can't pickle <class 'management.views.Stats'>: attribute lookup management.views.Stats failed Stats is a class i use to hold a couple of values, a string (user) and a number (calls), that are then used in a template. These are pickable, right? The data i want to pickle is the return value of this function: def calc_stats_topcallers(): stats_all = {} # cPickle doesn't like this class class Stats(object): def __init__(self): self.calls = None self.user = None current_year = datetime.datetime.now().year archive_year = current_year - 4 years = xrange(archive_year, current_year+1) for year in years: stats_year = [] counts = {} # Initialize count dict # If we don't do this, we get a KeyError for user in User.objects.all(): counts[user]=0 # Count the times an initiator has been calling for i in Call.objects.filter(date_created__year=year): for _init in i.initiator.all(): counts[_init] += 1 # Sort the dictionary count_sorted = sorted(counts.items(), lambda x, y: cmp(x[1], y[1]), reverse=True) # Take top 30 callers for user_stat in count_sorted[0:30]: if ( user_stat[1] > 0 ): st = Stats() st.calls = user_stat[1] st.user = user_stat[0] stats_year.append(st) stats_all[year]=stats_year stats_sorted = sorted(stats_all.items(), lambda x, y: cmp(x[0], y[0]), reverse=True) return stats_sorted When i run the function and pickle the data using a python shell, i get the error. How do i solve this as i haven't got a clue. Thanks, Benedict
From: Peter Otten on 3 Aug 2010 11:01 Benedict Verheyen wrote: > i get the following error when trying to set data in the cache of a django > application. The error is however a python error as it involves pickling > and i can reproduce it in a shell. > The error i get is this: > cPickle.PicklingError: Can't pickle <class 'management.views.Stats'>: > attribute lookup management.views.Stats failed > > Stats is a class i use to hold a couple of values, a string (user) and a > number (calls), that are then used in a template. These are pickable, > right? The data i want to pickle is the return value of this function: > > def calc_stats_topcallers(): > stats_all = {} > # cPickle doesn't like this class > class Stats(object): > def __init__(self): > self.calls = None > self.user = None You can only pickle instances of classes that are reachable by the import system as only the qualified name of the class is stored, not the bytecode to generate it. Move your class out of the function into the global module scope and you should be OK. Peter
From: Benedict Verheyen on 3 Aug 2010 11:37
On 3/08/2010 17:01, Peter Otten wrote: <snip> > You can only pickle instances of classes that are reachable by the import > system as only the qualified name of the class is stored, not the bytecode > to generate it. Move your class out of the function into the global module > scope and you should be OK. > > Peter Thanks Peter, that solved the problem ! Regards, Benedict |