Checks if data for this request has already been downloaded and is saved to disk.

        :return: returns ``True`` if data for this request has already been downloaded and is saved to disk.
        :rtype: bool

def is_downloaded(self):
        """ Checks if data for this request has already been downloaded and is saved to disk.

        :return: returns ``True`` if data for this request has already been downloaded and is saved to disk.
        :rtype: bool
        """
        if self.file_path is None:
            return False
        return os.path.exists(self.file_path)