Infinitely nested containers
steve+comp.lang.python at pearwood.info
Sat Nov 22 05:43:19 CET 2014
random832 at fastmail.us wrote:
> On Fri, Nov 21, 2014, at 02:00, Marko Rauhamaa wrote:
>> Gill Shen <gillarete at gmail.com>:
>> > How is this [nesting] behavior implemented under the hood?
>> > And why is this allowed at all?
>> There's no reason not to.
> There's no reason not to allow it with tuples, but you can't do it.
> Mainly because doing it in a single literal would require special
> syntax, whereas you can simply append to a list a reference to itself.
You can't append a list to itself in a single expression, you have to create
the list first.
> I think I tried on at least one python version and printing the tuple
> crashed with a recursion depth error, since it had no special protection
> for this case the way list printing does.
It works fine now (Python 3.3).
py> L = 
py> t = (L, None)
py> L.append(t) # For good measure.
([[...], (...)], None)
but yes, in old versions of Python printing self-recursive containers may
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