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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Fri, 21 Nov 2014 10:13:44 -0700
Subject: Re: Infinitely nested containers
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On Thu, Nov 20, 2014 at 10:54 PM, Gill Shen <gillarete@gmail.com> wrote:
> How is this behavior implemented under the hood? And why is this allowed at all? Is it just a curiosity or can you do something useful with it?

Reference cycles are common in Python and other OO languages. For
example, adding a widget to a window; the window contains references
to its child widgets, and it's probably useful for the widgets to know
what their parents are, so they would hold references back.

A list containing itself is similarly a reference cycle. I don't know
off-hand of any use for this specific case, but it's just a slightly
tighter cycle than normal.