code: def _expanded_sql(self):
      
      if not self._sql:
        self._sql = UDF._build_udf(self._name, self._code, self._return_type, self._params,
                                   self._language, self._imports)
      return self._sql
docs: Get the expanded BigQuery SQL string of this UDF
  
      Returns
        The expanded SQL string of this UDF