[Python-Dev] very slow compare of recursive objects (original) (raw)

Neal Norwitz neal@metaslash.com
Mon, 20 Jan 2003 10:50:17 -0500

On Mon, Jan 20, 2003 at 10:32:50AM -0500, Tim Peters wrote:

[Tim] >Tuples can't be recursive,

[Guido] > Oh yes they can be: > > >>> L = [] > >>> t = (L, L) > >>> L.append(L) > >>> That's an example of a tuple containing a recursive structure; there's still no way, starting at t, to get back to t. I think mutation is required for that. Like L = [None] t = (L, L) L[0] = t Then t[0]0] is t and that's what I mean by "recursive tuple" (a tuple that can be reached from itself).

What about:

    >>> t = ([],)
    >>> t[0].append(t)
    >>> print t
    ([([...],)],)
    >>> print t[0][0] is t
    True

Not sure if that's a tuple containing a recursive structure or a recursive tuple.

Neal