django postgres next/reset sequence id - https://gist.github.com/kissgyorgy/6110380 - http://stackoverflow.com/questions/244243/how-to-reset-postgres-primary-key-sequence-when-it-falls-out-of-sync

django_pg_sequence.py

from django.db import connection

def idseq(model_class):
    return '{}_id_seq'.format(model_class._meta.db_table)

def get_next_id(model_class):
    cursor = connection.cursor()
    sequence = idseq(model_class)
    cursor.execute("select nextval('%s')" % sequence)
    row = cursor.fetchone()
    cursor.close()
    return row[0]
    
def reset_sequence(model_class, value=1):
    cursor = connection.cursor()
    sequence = idseq(model_class)
    cursor.execute("ALTER SEQUENCE {} RESTART WITH {};".format(sequence, value))

def set_sequence(model):
    max_id = model.objects.aggregate(m=Max('id'))['m']
    seq = max_id or 1
    with connection.cursor() as cursor:
        cursor.execute("SELECT setval(pg_get_serial_sequence(%s,'id'), %s);", [model._meta.db_table, seq])

A bit shorter solution. Also it creates sequence if it does not exists. It was tested on PostgreSQL.