code: def get_slide(self, slide_id):
          
          for sldId in self._element.sldIdLst:
              if sldId.id == slide_id:
                  return self.related_parts[sldId.rId].slide
          return None
docs: Return the |Slide| object identified by *slide_id* (in this
          presentation), or |None| if not found.