code: def get_sum_of_quotas_as_dict(cls, scopes, quota_names=None, fields=['usage', 'limit']):
          
          if not scopes:
              return {}
  
          if quota_names is None:
              quota_names = cls.get_quotas_names()
  
          scope_models = set([scope._meta.model for scope in scopes])
          if len(scope_models) > 1:
              raise exceptions.QuotaError(_('All scopes have to be instances of the same model.'))
  
          filter_kwargs = {
              'content_type': ct_models.ContentType.objects.get_for_model(scopes[0]),
              'object_id__in': [scope.id for scope in scopes],
              'name__in': quota_names
          }
  
          result = {}
          if 'usage' in fields:
              items = Quota.objects.filter(**filter_kwargs)\
                           .values('name').annotate(usage=Sum('usage'))
              for item in items:
                  result[item['name'] + '_usage'] = item['usage']
  
          if 'limit' in fields:
              unlimited_quotas = Quota.objects.filter(limit=-1, **filter_kwargs)
              unlimited_quotas = list(unlimited_quotas.values_list('name', flat=True))
              for quota_name in unlimited_quotas:
                  result[quota_name] = -1
  
              items = Quota.objects\
                           .filter(**filter_kwargs)\
                           .exclude(name__in=unlimited_quotas)\
                           .values('name')\
                           .annotate(limit=Sum('limit'))
              for item in items:
                  result[item['name']] = item['limit']
  
          return result
docs: Return dictionary with sum of all scopes' quotas.
  
          Dictionary format:
          {
              'quota_name1': 'sum of limits for quotas with such quota_name1',
              'quota_name1_usage': 'sum of usages for quotas with such quota_name1',
              ...
          }
          All `scopes` have to be instances of the same model.
          `fields` keyword argument defines sum of which fields of quotas will present in result.