Skip Montanaro <skip@mojam.com>:
Can someone give me an example where this is actually useful and can't be handled through some existing mechanism?
I can envisage cases where you want to build a data structure incrementally, and then treat it as immutable so you can use it as a dict key, etc. There's currently no way to do that to a list without copying it. So, it could be handy to have a way of turning a list into a tuple in-place. It would have to be a one-way transformation, otherwise you could start using it as a dict key, make it mutable again, and cause havoc. Suggested implementation: When you allocate the space for the values of a list, leave enough room for the PyObject_HEAD of a tuple at the beginning. Then you can turn that memory block into a real tuple later, and flag the original list object as immutable so you can't change it later via that route. Hmmm, would waste a bit of space for each list object. Maybe this should be a special list-about-to-become-tuple type. (Tist? Luple?) Greg Ewing, Computer Science Dept, +--------------------------------------+ University of Canterbury, | A citizen of NewZealandCorp, a | Christchurch, New Zealand | wholly-owned subsidiary of USA Inc. | greg@cosc.canterbury.ac.nz +--------------------------------------+