def output(self, stream, value):
if stream not in self.outputs:<EOL><INDENT>raise ValueError("<STR_LIT>")<EOL><DEDENT>e = self.expression(value)<EOL>e._stream = stream<EOL>return e<EOL>
SPL output port assignment expression.

        Arguments:
            stream(Stream): Output stream the assignment is for.
            value(str): SPL expression used for an output assignment. This can be a string, a constant, or an :py:class:`Expression`.

        Returns:
            Expression: Output assignment expression that is valid as a the context of this operator.