code: def set_polar_box(self, rmin=0, rmax=1, tmin=0, tmax=2 * pi):
          
          self._rmin = rmin
          self._rmax = rmax
          self._tmin = tmin
          self._tmax = tmax
          self.xmin = self.ymin = rmin - rmax
          self.xmax = self.ymax = rmax - rmin
docs: Helper for polar charts