Editing south migrations to run custom sql

migrations.py

# -*- coding: utf-8 -*-
import datetime
from south.db import db
from south.v2 import DataMigration
from django.db import models

class Migration(DataMigration):

    def forwards(self, orm):
        db.start_transaction()
        db.execute("""
            UPDATE table_name
            SET myfield = ('x' || lpad(browser_id,16,'0'))::bit(64)::bigint #converts hex to bigint in sql
            WHERE myfield IS NOT NULL;
        """)
        db.commit_transaction()
        db.start_transaction()
        db.execute("ALTER TABLE table_name DROP COLUMN old_field")
        db.commit_transaction()

    def backwards(self, orm):
        pass