Multiple images in a HIT with python API

Hello,
I am trying to create a HIT in MTurk using the python API. Let say a single HIT has 3 images. How would I modify the api call mturk.create_hit to replace the URL of the 3 images in my XML code? I believe the call is something like this:
.....
response = mturk.create_hit(**task_attributes,
Question = questions_xml.replace('${image_url}', ....))
hit_type_id = response['HIT']['HITTypeId'] ....

So basically, how would I change the 'Question' attribute to replace the 3 image_url?
Thanks