code: def _InitializeURL(self, upload_url, current_content_length):
      
      # If initialization is not necessary, return the provided upload_url.
      if current_content_length != 0:
        return upload_url
  
      headers = {
          'Content-Type': 'application/xml',
          'Content-Length': 0,
          'x-goog-resumable': 'start'
      }
  
      # Send an HTTP POST request to the given upload_url
      req = urllib2.Request(upload_url, data={}, headers=headers)
      resp = self._url_opener.open(req)
  
      return resp.headers['location']
docs: Ensures that the URL used to upload operations is properly initialized.
  
      Args:
        upload_url: a string url.
        current_content_length: an integer identifying the current content length
          of data uploaded to the Batch Job.
  
      Returns:
        An initialized string URL, or the provided string URL if the URL has
        already been initialized.