Generates a symmetry of the Polyhedron respect global axes.
        
        :param axes: 'x', 'y', 'z', 'xy', 'xz', 'yz'...
        :type axes: str
        :returns: ``pyny.Polyhedron``

def mirror(self, axes='x'):
        """
        Generates a symmetry of the Polyhedron respect global axes.
        
        :param axes: 'x', 'y', 'z', 'xy', 'xz', 'yz'...
        :type axes: str
        :returns: ``pyny.Polyhedron``
        """
        polygon = np.array([[0,0], [0,1], [1,1]])
        space = Space(Place(polygon, polyhedra=self))
        return space.mirror(axes, inplace=False)[0].polyhedra[0]