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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def end_parallel(self):
 """ Ends a parallel region by merging the channels into a single stream. Returns: Stream: Stream for which subsequent transformations are no longer parallelized. .. seealso:: :py:meth:`set_parallel`, :py:meth:`parallel` """

        outport = self.oport
        if isinstance(self.oport.operator, streamsx.topology.graph.Marker):
            if self.oport.operator.kind == "$Union$":
                pto = self.topology.graph.addPassThruOperator()
                pto.addInputPort(outputPort=self.oport)
                outport = pto.addOutputPort(schema=self.oport.schema)
        op = self.topology.graph.addOperator("$EndParallel$")
        op.addInputPort(outputPort=outport)
        oport = op.addOutputPort(schema=self.oport.schema)
        endP = Stream(self.topology, oport)
        return endP