code: def _update_example(self, request):
      
      if request.method != 'POST':
        return http_util.Respond(request, {'error': 'invalid non-POST request'},
                                 'application/json', code=405)
      example_json = request.form['example']
      index = int(request.form['index'])
      if index >= len(self.examples):
        return http_util.Respond(request, {'error': 'invalid index provided'},
                                 'application/json', code=400)
      new_example = self.example_class()
      json_format.Parse(example_json, new_example)
      self.examples[index] = new_example
      self.updated_example_indices.add(index)
      self.generate_sprite([ex.SerializeToString() for ex in self.examples])
      return http_util.Respond(request, {}, 'application/json')
docs: Updates the specified example.
  
      Args:
        request: A request that should contain 'index' and 'example'.
  
      Returns:
        An empty response.