Get all (single column and multi column) unique constraints

def _unique_constrains(cls):
        """Get all (single column and multi column) unique constraints"""
        unique = [{c.name for c in u.columns} for u in cls.__table_args__
                  if isinstance(u, UniqueConstraint)]
        unique.extend({c.name} for c in cls.__table__.columns if c.unique)
        return unique