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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 add_workflow(self, workflow):
 """ Add a sub-workflow to this workflow This function adds a sub-workflow of Workflow class to this workflow. Parent child relationships are determined by data dependencies Parameters workflow : Workflow instance The sub-workflow to add to this one """

        workflow.in_workflow = self
        self.sub_workflows += [workflow]

        node = workflow.as_job
        self._adag.addJob(node)

        node.file.PFN(os.path.join(os.getcwd(), node.file.name), site='local')
        self._adag.addFile(node.file)

        for inp in self._external_workflow_inputs:
            workflow._make_root_dependency(inp.node)

        return self