code: def download(self):
          
          mp3_directory = self._pre_download()
          self.data.swifter.apply(func=lambda arg: self._download(*arg, mp3_directory), axis=1, raw=True)
          return mp3_directory
docs: Downloads the data associated with this instance
          Return:
            mp3_directory (os.path): The directory into which the associated mp3's were downloaded