def attribute(self, stream, name):
if stream not in self._inputs:<EOL><INDENT>raise ValueError("<STR_LIT>")<EOL><DEDENT>if len(self._inputs) == <NUM_LIT:1>:<EOL><INDENT>return Expression('<STR_LIT>', name)<EOL><DEDENT>else:<EOL><INDENT>iport = self._op().inputPorts[self._inputs.index(stream)]<EOL>return Expression('<STR_LIT>', iport._alias + '<STR_LIT:.>' + name)<EOL><DEDENT>
Expression for an input attribute.

        An input attribute is an attribute on one of the input
        ports of the operator invocation. `stream` must have been
        used to declare this invocation.

        Args:
            stream(Stream): Stream the attribute is from.
            name(str): Name of the attribute.

        Returns:
            Expression: Expression representing the input attribute.