Return the |Slide| object identified by *slide_id* (in this
        presentation), or |None| if not found.

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