@classmethod
def download_and_prepare(cls, levels=None):
    """Downloads dataset from Kaggle, extracts zip files
    and processes it using `tensorflow_datasets`.
    
    Args:
      levels: (optional) `iterable` of `str`, specifies which
        levels from {'medium', 'realworld'} to prepare,
        if None it prepares all the levels.

    Raises:
      OSError: if `~/.kaggle/kaggle.json` is not set up. 
    """
    import os
    os.environ['CUDA_VISIBLE_DEVICES'] = '-1'
    cls._download()
    cls._extract()
    cls._prepare(levels)
