code: def get_link_href(result_object, link_relation):
      
  
      # Argument error checking.
      assert result_object is not None
  
      result = None
  
      link = result_object['_links'].get(link_relation)
      if link:
          result = link.get('href')
  
      return result
docs: Given a result_object (returned by a previous API call), return
      the link href for a link relation.
  
      'result_object' a JSON object returned by a previous API call. May not
      be None.
      'link_relation' the link relation for which href is required.
  
      Returns None if the link does not exist.