SQLAlchemy get or create

get_or_create.py

def get_or_create(session, model, defaults=None, **kwargs):
	"""
	Get or create a model instance while preserving integrity.
	"""
	try:
		return session.query(model).filter_by(**kwargs).one(), False
	except NoResultFound:
		if defaults is not None:
			kwargs.update(defaults)
		try:
			with session.begin_nested():
				instance = model(**kwargs)
				session.add(instance)
				return instance, True
		except IntegrityError:
			return session.query(model).filter_by(**kwargs).one(), False

You don't need begin_nested block here, since there's just one write operation being made. Instead, session.commit() after L14 would do it.

Commit is needed for changes to be persisted in DB, and id to be available in the instance.