The documentation of Sequence.set_immutable() is quite clear. "Never" means that there is no way:
Definition: Sequence.set_immutable(self) Docstring: Make this object immutable, so it can never again be changed. EXAMPLES: sage: v = Sequence([1,2,3,4/5]) sage: v[0] = 5 sage: v [5, 2, 3, 4/5] sage: v.set_immutable() sage: v[3] = 7 Traceback (most recent call last): ... ValueError: object is immutable; please change a copy instead. -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org