Similar to urllib.urlretrieve or urllib.request.urlretrieve
        only that *filname* is required.

        :param url: URL to download.
        :param filename: Filename to save the content to.
        :param data: Valid URL-encoded data.
        :return: Tuple containing path and headers.

def urlretrieve(self, url, filename, data=None):
        """
        Similar to urllib.urlretrieve or urllib.request.urlretrieve
        only that *filname* is required.

        :param url: URL to download.
        :param filename: Filename to save the content to.
        :param data: Valid URL-encoded data.
        :return: Tuple containing path and headers.
        """
        logger.info('saving: \'%s\' to \'%s\'', url, filename)

        if _is_py3:
            return _urlretrieve_with_opener(self.opener, url, filename, data=data)

        return self.opener2.retrieve(url, filename, data=data)