code: def expand_dims(self, axis):
          
          if axis <= self._distaxis:
              subaxis = axis
              new_distaxis = self._distaxis + 1
          else:
              subaxis = axis - 1
              new_distaxis = self._distaxis
          new_subts = [rts.expand_dims(subaxis) for rts in self._subarrays]
          if axis == 0:
              # prepended an axis: no longer a Timeseries
              return distob.DistArray(new_subts, new_distaxis)
          else:
              axislabels = self.labels[self._distaxis]
              return DistTimeseries(new_subts, new_distaxis, axislabels)
docs: Insert a new axis, at a given position in the array shape
          Args:
            axis (int): Position (amongst axes) where new axis is to be inserted.