[Python-ideas] add a list.swap() method

Kristján Valur Jónsson kristjan at ccpgames.com
Fri Jun 26 14:05:23 CEST 2009

> -----Original Message-----
> From: python-ideas-bounces+kristjan=ccpgames.com at python.org
> [mailto:python-ideas-bounces+kristjan=ccpgames.com at python.org] On
> Behalf Of Nick Coghlan
> Sent: 26. júní 2009 09:06
> To: Steven D'Aprano
> Cc: python-ideas at python.org
> Subject: Re: [Python-ideas] add a list.swap() method
> I think Kristján's point was that list.pop() and friends don't perform
> a
> PyList_CheckExact on themselves before following their fast path
> implementation so they can bypass custom get/set/del methods in
> subclasses.

Right.  I've already agreed that my suggestion idea is too radical.  I'm merely observing that our discussion has pointed out that other list member functions can be dangerous for list subclasses since they too perform "magic shortcuts" to achieve their goal.
So, those that write list subclasses that maintain internal state based on their members, must be careful to override all of these magic list functions.  They are list.append, list.pop, list.reverse, list.sort, list.insert, that I can see with a casual perusal of the source.
In particular, append(), pop() and insert() modify the list length, which might confuse some subclasses.



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