On 18/08/2012 21:29, Aaron Brady wrote:
On Friday, August 17, 2012 4:57:41 PM UTC-5, Chris Angelico wrote:
On Sat, Aug 18, 2012 at 4:37 AM, Aaron Brady <castiro...@gmail.com> wrote:
> Is there a problem with hacking on the Beta?
Nope. Hack on the beta, then when the release arrives, rebase your
work onto it. I doubt that anything of this nature will be changed
between now and then.
ChrisA
Thanks Chris, your post was encouraging.
I have a question about involving the 'tp_clear' field of the types.
http://docs.python.org/dev/c-api/typeobj.html#PyTypeObject.tp_clear
'''
...The tuple type does not implement a tp_clear function, because it’s possible
to prove that no reference cycle can be composed entirely of tuples.
'''
I didn't follow the reasoning in the proof; the premise is necessary but IMHO
not obviously sufficient. Nevertheless, the earlier diagram contains an overt
homogeneous reference cycle.
Reposting:
http://home.comcast.net/~castironpi-misc/clpy-0062%20set%20iterators.png
In my estimate, the 'tp_traverse' and 'tp_clear' fields of the set doesn't need
to visit the auxiliary collection; the same fields of the iterators don't need
to visit the primary set or other iterators; and references in the linked list
don't need to be included in the iterators' reference counts.
Can someone who is more familiar with the cycle detector and cycle breaker,
help prove or disprove the above?
In simple terms, when you create an immutable object it can contain
only references to pre-existing objects, but in order to create a cycle
you need to make an object refer to another which is created later, so
it's not possible to create a cycle out of immutable objects.
However, using Python's C API it _is_ possible to create such a cycle,
by mutating an otherwise-immutable tuple (see PyTuple_SetItem and
PyTuple_SET_ITEM).
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