[Tutor] list of dicts <-> dict of lists?

[spir ☣]

On Thu, 27 May 2010 20:00:46 -0600
Matthew Wood <woodm1979 at gmail.com> wrote:

> I THOUGHT the guaranteed same-ordering of dict.keys and dict.values started
> in python 2.6.  That was a simple mistake.
> 
> It turns out, that's not the case.  But in general, access to dicts and sets
> is unordered, so you can't/don't/shouldn't count on ordering.  The solution
> to take keys and values from dict.items() DOES guarantee their ordering,
> even if dict.keys and dict.values aren't.

The word "order" is a bit over-used :-)
Python's guarantee is that the *output* orders of keys() & value() match each other. Say, they're consistent // sequences. This is a different feature from preserving *input* order of of keys, or of key:value pairs. (Which is not true is Python or Lua, for instance, but in recent Ruby versions, yes: http://www.igvita.com/2009/02/04/ruby-19-internals-ordered-hash/.)

Denis
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