def with_variant(self, type_, dialect_name):
        """Return a new :class:`.Variant` which adds the given
        type + dialect name to the mapping, in addition to the
        mapping present in this :class:`.Variant`.

        :param type_: a :class:`.TypeEngine` that will be selected
         as a variant from the originating type, when a dialect
         of the given name is in use.
        :param dialect_name: base name of the dialect which uses
         this type. (i.e. ``'postgresql'``, ``'mysql'``, etc.)

        """

        if dialect_name in self.mapping:
            raise exc.ArgumentError(
                "Dialect '%s' is already present in "
                "the mapping for this Variant" % dialect_name)
        mapping = self.mapping.copy()
        mapping[dialect_name] = type_
        return Variant(self.impl, mapping)
dataset/ETHPy150Open goFrendiAsgard/kokoropy/kokoropy/packages/sqlalchemy/sql/type_api.py/Variant.with_variant/original