download.py 文件源码

def _DownloadFile(self, url, max_retries=5, show_progress=None):
    """Downloads a file from and saves it to the specified location.

    Args:
      url:  The address of the file to be downloaded.
      max_retries:  The number of times to attempt to download
        a file if the first attempt fails.
      show_progress: Print download progress to stdout (overrides default).

    Raises:
      DownloadError: The downloaded file did not match the expected file
        size.
    """
    attempt = 0
    file_stream = None

    opener = urllib2.OpenerDirector()
    for handler in self._GetHandlers():
      opener.add_handler(handler)
    urllib2.install_opener(opener)

    while True:
      try:
        attempt += 1
        file_stream = urllib2.urlopen(url)
      except urllib2.HTTPError:
        logging.error('File not found on remote server: %s.', url)
      except urllib2.URLError as e:
        logging.error('Error connecting to remote server to download file '
                      '"%s". The error was: %s', url, e)
      if file_stream:
        if file_stream.getcode() in [200]:
          break
        else:
          raise DownloadError('Invalid return code for file %s. [%d]' %
                              (url, file_stream.getcode()))

      if attempt < max_retries:
        logging.info('Sleeping for 20 seconds and then retrying the download.')
        time.sleep(20)
      else:
        raise DownloadError('Permanent download failure for file %s.' % url)

    self._StreamToDisk(file_stream, show_progress)