'Generate a histogram object and store in the specified attribute.'

def Save(self, cron_flow):

    histograms = {}
    for active_time in self.active_days:
        for label in self.categories[active_time].keys():
            histograms.setdefault(label, self.attribute())
            graph = rdfstats.Graph(title=('%s    day    actives    for    %s    label' % (active_time, label)))
            for (k, v) in sorted(self.categories[active_time][label].items()):
                graph.Append(label=k, y_value=v)
            histograms[label].Append(graph)
    for (label, histogram) in histograms.items():
        cron_flow._StatsForLabel(label).AddAttribute(histogram)
