Download the dataset.

def _download_movielens(dest_path):
    """
    Download the dataset.
    """

    url = 'http://files.grouplens.org/datasets/movielens/ml-100k.zip'
    req = requests.get(url, stream=True)

    with open(dest_path, 'wb') as fd:
        for chunk in req.iter_content():
            fd.write(chunk)