Return the slide identifier associated with *slide_part* in this
        presentation.

def slide_id(self, slide_part):
        """
        Return the slide identifier associated with *slide_part* in this
        presentation.
        """
        for sldId in self._element.sldIdLst:
            if self.related_parts[sldId.rId] is slide_part:
                return sldId.id
        raise ValueError('matching slide_part not found')