type_api.py 文件源码

def with_variant(self, type_, dialect_name):
        """Produce a new type object that will utilize the given
        type when applied to the dialect of the given name.

        e.g.::

            from sqlalchemy.types import String
            from sqlalchemy.dialects import mysql

            s = String()

            s = s.with_variant(mysql.VARCHAR(collation='foo'), 'mysql')

        The construction of :meth:`.TypeEngine.with_variant` is always
        from the "fallback" type to that which is dialect specific.
        The returned type is an instance of :class:`.Variant`, which
        itself provides a :meth:`.Variant.with_variant`
        that can be called repeatedly.

        :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.)

        .. versionadded:: 0.7.2

        """
        return Variant(self, {dialect_name: to_instance(type_)})