Find duplicates in queryset

gistfile1.py

from django.db.models import Count

def duplicates_by(model, field):
    values = model.objects\
        .values(field)\
        .annotate(Count(field))\
        .order_by(field)\
        .filter(**{'%s__count__gt' % field: 1})\
        .values_list(field, flat=True)

    return model.objects.filter(**{'%s__in' % field: values}).order_by(field)