def _on_calculate_verts(self):
        self.u_interval = self.intervals[0]
        self.u_set = list(self.u_interval.frange())
        self.v_interval = self.intervals[1]
        self.v_set = list(self.v_interval.frange())
        self.bounds = [[S.Infinity, -S.Infinity, 0],
                       [S.Infinity, -S.Infinity, 0],
                       [S.Infinity, -S.Infinity, 0]]
        evaluate = self._get_evaluator()

        self._calculating_verts_pos = 0.0
        self._calculating_verts_len = float(
            self.u_interval.v_len*self.v_interval.v_len)

        verts = list()
        b = self.bounds
        for u in self.u_set:
            column = list()
            for v in self.v_set:
                try:
                    _e = evaluate(u, v)  # calculate vertex
                except ZeroDivisionError:
                    _e = None
                if _e is not None:  # update bounding box
                    for axis in range(3):
                        b[axis][0] = min([b[axis][0], _e[axis]])
                        b[axis][1] = max([b[axis][1], _e[axis]])
                column.append(_e)
                self._calculating_verts_pos += 1.0

            verts.append(column)
        for axis in range(3):
            b[axis][2] = b[axis][0] - b[axis][1]
            if b[axis][2] == 0.0:
                b[axis][2] = 1.0

        self.verts = verts
        self.push_wireframe(self.draw_verts(False, False))
        self.push_solid(self.draw_verts(False, True))
dataset/ETHPy150Open sympy/sympy/sympy/plotting/pygletplot/plot_surface.py/PlotSurface._on_calculate_verts/swapped operands of `-`