<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def chart_part(self):
 """ The |ChartPart| object containing the chart in this graphic frame. """

        rId = self._element.chart_rId
        chart_part = self.part.related_parts[rId]
        return chart_part