Take points (z,x,q) and sort by increasing z

def sort_points(self, points):
        """Take points (z,x,q) and sort by increasing z"""
        new_points = []
        z_lookup = {}
        for z, x, Q in points:
            z_lookup[z] = (z, x, Q)

        z_keys = z_lookup.keys()
        z_keys.sort()

        for key in z_keys:
            new_points.append(z_lookup[key])

        return new_points