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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 CIFAR-10 dataset file. The CIFAR-10 dataset file is downloaded from Alex Krizhevsky's website [ALEX]. Parameters subparser : :class:`argparse.ArgumentParser` Subparser handling the `cifar10` command. """

    url = 'http://www.cs.toronto.edu/~kriz/cifar-10-python.tar.gz'
    filename = 'cifar-10-python.tar.gz'
    subparser.set_defaults(urls=[url], filenames=[filename])
    return default_downloader