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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 dump_viewset(viewset_class, root_folder, folder_fn=lambda i: ".", sample_size=None):
 """ Dump the contents of a rest-api queryset to a folder structure. :param viewset_class: A rest-api viewset to iterate through :param root_folder: The root folder to write results to. :param folder_fn: A function to generate a subfolder name for the instance. :param sample_size: Number of items to process, for test purposes. :return: """

    if os.path.exists(root_folder):
        shutil.rmtree(root_folder)
    os.makedirs(root_folder)

    vs = viewset_class()
    vs.request = rf.get('')

    serializer_class = vs.get_serializer_class()
    serializer = serializer_class(context={'request': vs.request, 'format': 'json', 'view': vs})

    renderer = PrettyJSONRenderer()

    bar = progressbar.ProgressBar()
    for instance in bar(vs.get_queryset()[:sample_size]):
        dct = serializer.to_representation(instance)
        content = renderer.render(dct)
        folder = os.path.join(root_folder, folder_fn(instance))
        if not os.path.exists(folder):
            os.makedirs(folder)
        filename = "%s.json" % instance.slug

        f = file(os.path.join(folder, filename), 'w')
        f.write(content)
        f.close()