code: def calculateValues(self):
          
          chart = self.chart()
          if not chart:
              return super(XDatasetAxis, self).calculateValues()
          else:
              values = []
              for dataset in chart.datasets():
                  values.append(dataset.name())
              values.sort()
              return values
docs: Overloads the calculate values method to calculate the values for
          this axis based on the minimum and maximum values, and the number
          of steps desired.
          
          :return     [<variant>, ..]