human
Complete this python program:
def _FetchLog(http_client, log_url, output_file, callback):
assistant
#Here is the Python program you requested.

    """Fetches the log file at "log_url" and stores it in
    "output_file".
    """
    def _OnFetch(response):
        if (response.code == 200):
            with open(output_file, 'w') as f:
                f.write(response.body)
                logging.info(('wrote    %d    bytes    to    %s' % (len(response.body), output_file)))
        else:
            logging.error(('failed    to    fetch    %s' % log_url))
        callback()
    http_client.fetch(log_url, callback=_OnFetch, method='GET')