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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 fill_subparser(subparser):
 """Sets up a subparser to download the binarized MNIST dataset files. The binarized MNIST dataset files (`binarized_mnist_{train,valid,test}.amat`) are downloaded from Hugo Larochelle's website [HUGO]. .. [HUGO] http://www.cs.toronto.edu/~larocheh/public/datasets/ binarized_mnist/binarized_mnist_{train,valid,test}.amat Parameters subparser : :class:`argparse.ArgumentParser` Subparser handling the `binarized_mnist` command. """

    sets = ['train', 'valid', 'test']
    urls = ['http://www.cs.toronto.edu/~larocheh/public/datasets/' +
            'binarized_mnist/binarized_mnist_{}.amat'.format(s) for s in sets]
    filenames = ['binarized_mnist_{}.amat'.format(s) for s in sets]
    subparser.set_defaults(urls=urls, filenames=filenames)
    return default_downloader