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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 update(client, revision, no_output, siblings, paths):
 """Update existing files by rerunning their outdated workflow."""

    graph = Graph(client)
    outputs = graph.build(revision=revision, can_be_cwl=no_output, paths=paths)
    outputs = {node for node in outputs if graph.need_update(node)}

    if not outputs:
        click.secho(
            'All files were generated from the latest inputs.', fg='green'
        )
        sys.exit(0)

    # Check or extend siblings of outputs.
    outputs = siblings(graph, outputs)
    output_paths = {node.path for node in outputs if _safe_path(node.path)}

    # Get all clean nodes.
    input_paths = {node.path for node in graph.nodes} - output_paths

    # Store the generated workflow used for updating paths.
    import yaml

    output_file = client.workflow_path / '{0}.cwl'.format(uuid.uuid4().hex)
    workflow = graph.ascwl(
        input_paths=input_paths,
        output_paths=output_paths,
        outputs=outputs,
    )

    # Make sure all inputs are pulled from a storage.
    client.pull_paths_from_storage(
        *(path for _, path in workflow.iter_input_files(client.workflow_path))
    )

    with output_file.open('w') as f:
        f.write(
            yaml.dump(
                ascwl(
                    workflow,
                    filter=lambda _, x: x is not None,
                    basedir=client.workflow_path,
                ),
                default_flow_style=False
            )
        )

    from ._cwl import execute
    execute(client, output_file, output_paths=output_paths)