title: Parallelize get_serving_url in GAE Python
body: <p>The <a href="https://cloud.google.com/cloud-trace/" rel="nofollow noreferrer">Traces</a> graph showed <code>/images.GetUrlBase</code> calls for my search function. I tried to make it call <code>get_serving_url ()</code> in parallel but still the <a href="https://cloud.google.com/cloud-trace/" rel="nofollow noreferrer">Traces</a> graph shows the calls as sequential.<br>
  How do I make it parallel ? </p>
  
  <p><a href="https://i.stack.imgur.com/JZABo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JZABo.png" alt="enter image description here"></a> </p>
  
  <p><strong>My Attempt</strong>  </p>
  
  <pre><code>class Gets 
      @staticmethod 
      @ndb.tasklet 
      def get_img_url_parallel ( image_key ): 
          url     = yield images.get_serving_url_async (image_key) 
          raise ndb.Return ( url ) 
  
  
  @toplevel 
  def search (..): 
      :: 
      for record in record_list: 
          :: 
          for photo in record.photo_list: 
              if (photo != ""): 
                  yielded_photo   = yield Gets.get_img_url_parallel ( photo ) 
                  photo_list.append ( yielded_photo  ) 
  ::
  </code></pre>
  
  <p>I am new to yield, tasklet. </p>