code: def _compute(self):
          
          delta = 2 * pi / self._len if self._len else 0
          self._x_pos = [.5 * pi + i * delta for i in range(self._len + 1)]
          for serie in self.all_series:
              serie.points = [(v, self._x_pos[i])
                              for i, v in enumerate(serie.values)]
              if self.interpolate:
                  extended_x_pos = ([.5 * pi - delta] + self._x_pos)
                  extended_vals = (serie.values[-1:] + serie.values)
                  serie.interpolated = list(
                      map(
                          tuple,
                          map(
                              reversed,
                              self._interpolate(extended_x_pos, extended_vals)
                          )
                      )
                  )
  
          # x labels space
          self._box.margin *= 2
          self._rmin = self.zero
          self._rmax = self._max or 1
          self._box.set_polar_box(self._rmin, self._rmax)
          self._self_close = True
docs: Compute r min max and labels position