Version with the most downloads.

        :return: A tuple of the form (version, n_downloads)

def max_version(self):
        """Version with the most downloads.

        :return: A tuple of the form (version, n_downloads)
        """
        data = self.version_downloads
        if not data:
            return None, 0
        return max(data.items(), key=lambda item: item[1])