def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def make_data(cuda=False):
    train_x = torch.linspace(0, 1, 100)
    train_y = torch.sin(train_x * (2 * pi))
    train_y.add_(torch.randn_like(train_y), alpha=1e-2)
    test_x = torch.rand(51)
    test_y = torch.sin(test_x * (2 * pi))
    if cuda:
        train_x = train_x.cuda()
        train_y = train_y.cuda()
        test_x = test_x.cuda()
        test_y = test_y.cuda()
    return train_x, train_y, test_x, test_y