@_generative
    def where(self, whereclause):
        if self._whereclause is not None:
            self._whereclause = and_(self._whereclause,
                                     _literal_as_text(whereclause))
        else:
            self._whereclause = _literal_as_text(whereclause)
return a new update() construct with the given expression added to
dataset/ETHPy150Open zzzeek/sqlalchemy/lib/sqlalchemy/sql/dml.py/Update.where