obj in list and list ids the same

[Neel Krishnaswami]

rdudfield at my-deja.com <rdudfield at my-deja.com> wrote:
>Hello,
>
>I've got a problem where a list has the same id as a object instance in that
>same list.  This is as returned by id().
>
>Is this ever supposed to happen?  I just thought this was odd.	This happens
>when I am trying to copy a list of objects (sheets ) in the current object
>into a object which is also in a list( not the same one).  Then I try to copy
>a object (shape) from a global list into a list inside a sheet object which
>is inside a list in the node object.

If the id()'s are the same, then you have managed to create a circular
reference in your list. Eg:

  Python 1.5.2 (#8, May 12 1999, 17:46:31)  [GCC 2.7.2.1] on linux2
  Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
  >>> x = []
  >>> x.append(x) # create a circular reference

  >>> id(x)
  135060792

  >>> id(x[0])
  135060792

Double-check your code to make sure that the list assignments can
never reference themselves (unless that's what it's supposed to do, of
course). Lots of can't-happen cases turn out to actually be possible
when the code is run. :(

Note that circular references can't be automatically garbage-collected
under CPython -- only Viper and JPython can currently gc circular
references. This isn't normally a problem unless you create a *lot* of
circular garbage, or if the script will run for a long time (like as a
daemon process).


Neel