On Tue, Jun 23, 2009, Raymond Hettinger wrote:
[Kristj?n Valur J?nsson]
The idea is to speed up the swapping of list elemenst so that a.swap(b) is equivalent to a[:], b[:] = b[:], a[:] but without all the overhead of creating slices, assigning them and so forth.
The problem with the OP's example is that it only makes sense in interactions between a list and a list subclass that won't be broken by it. For straight list-to-list interactions, it is better to write "a,b = b,a" (though this is not exactly the same thing since the identity of a and b will change, not just their contents). For list subclass uses (a more advanced topic), some example will work and some won't (I gave two failing examples in the tracker discussion). When the list subclass is a C extension written by a third-party, it may not be possible to know whether or not a swap will break invariants. That's a killer.
Thanks for the detailed response and explanation of why Kristjan wants the feature and why it isn't the same thing as the standard tuple swap. Your assessment makes sense, and I agree that this doesn't belong as a standard list feature. -- Aahz (aahz@pythoncraft.com) <*> http://www.pythoncraft.com/ "as long as we like the same operating system, things are cool." --piranha