gistfile1.py

class CreationMixin():

    @classmethod
    def add(cls, session, *args, **kwargs):
        with transaction.manager:
            session.add(cls, *args, **kwargs)
      
class Labels(Base, CreationMixin):

    __tablename__ = 'labels'
    id = Column(Integer, primary_key=True)

    contents = Column(Unicode)
    description = Column(Unicode)

# usage:

label = Labels.add(
    session = DBSession,
    name = 'My Label',
    description = 'Very Important',
)