MongoKit: Auto Increment

sequential.py

from mongokit import Document

class Sequential(Document):
    __collection__ = 'sequential'

    structure = {
        '_id': basestring,
        'next': long
    }
    indexes = [{ 'fields': ['_id'], 'unique': True }]

    @classmethod
    def reset(cls, db, type, start=1):
        db.sequential.find_and_modify(
            query={'_id': type},
            update={'next': long(start - 1)},
            upsert=True,
            new=True)

    @classmethod
    def next(cls, db, type):
        return db.sequential.find_and_modify(
            query={'_id': type},
            update={'$inc': {'next': long(1)}},
            upsert=True,
            new=True)['next']

if __name__ == '__main__':
    from mongokit import Connection
    db = Connection(host='localhost', port=27017)['test']
    Sequential.reset(db, 'id', 1) #Optional
    assert Sequential.next(db, 'id') == 1, 'Invalid sequential'
    assert Sequential.next(db, 'id') == 2, 'Invalid sequential'
    assert Sequential.next(db, 'id') == 3, 'Invalid sequential'
    Sequential.reset(db, 'id', 2)
    assert Sequential.next(db, 'id') == 2, 'Invalid sequential'