type_api.py 文件源码

def _adapt_expression(self, op, other_comparator):
            """evaluate the return type of <self> <op> <othertype>,
            and apply any adaptations to the given operator.

            This method determines the type of a resulting binary expression
            given two source types and an operator.   For example, two
            :class:`.Column` objects, both of the type :class:`.Integer`, will
            produce a :class:`.BinaryExpression` that also has the type
            :class:`.Integer` when compared via the addition (``+``) operator.
            However, using the addition operator with an :class:`.Integer`
            and a :class:`.Date` object will produce a :class:`.Date`, assuming
            "days delta" behavior by the database (in reality, most databases
            other than PostgreSQL don't accept this particular operation).

            The method returns a tuple of the form <operator>, <type>.
            The resulting operator and type will be those applied to the
            resulting :class:`.BinaryExpression` as the final operator and the
            right-hand side of the expression.

            Note that only a subset of operators make usage of
            :meth:`._adapt_expression`,
            including math operators and user-defined operators, but not
            boolean comparison or special SQL keywords like MATCH or BETWEEN.

            """
            return op, self.type