<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def ylim(self, low, high):
 """Set yaxis limits Parameters low : number high : number index : int, optional Returns ------- Chart """

        self.chart['yAxis'][0]['min'] = low
        self.chart['yAxis'][0]['max'] = high
        return self