def process(self, lookup_type, value, connection):
        """
        Returns a tuple of data suitable for inclusion in a WhereNode
        instance.
        """
        # Because of circular imports, we need to import this here.
        from django.db.models.base import ObjectDoesNotExist
        try:
            if self.field:
                params = self.field.get_db_prep_lookup(lookup_type, value,
                    connection=connection, prepared=True)
                db_type = self.field.db_type(connection=connection)
            else:
                # This branch is used at times when we add a comparison to NULL
                # (we don't really want to waste time looking up the associated
                # field object at the calling location).
                params = Field().get_db_prep_lookup(lookup_type, value,
                    connection=connection, prepared=True)
                db_type = None
        except __HOLE__:
            raise EmptyShortCircuit

        return (self.alias, self.col, db_type), params
dataset/ETHPy150Open daoluan/decode-Django/Django-1.5.1/django/db/models/sql/where.py/Constraint.process