example.py

def db_transaction(flush=False):
    """
    Takes care of rolling back, committing and closing
    session for decorated function.
    """
    def wrap(f):
        def wrapped_f(*args, **kwargs):
            session = kwargs.get('session')
            try:
                result = f(*args, **kwargs)
            except Exception:
                session.rollback()
                raise
            finally:
                if flush:
                    session.flush()
                session.commit()
                session.close()
                
                return result
        return wrapped_f
    return wrap

@db_transaction(flush=True)
def add_model(model, session=Session()):
    session.add(model)
    return model