On 1/23/2009 2:49 AM, Chris Rebert wrote:
On Thu, Jan 22, 2009 at 5:41 PM, Giovanni Bajo <ra...@develer.com> wrote:
On Thu, 22 Jan 2009 10:11:37 -0800, Raymond Hettinger wrote:
The collections module in Python 2.7 and Python 3.1 has gotten a new
Counter class that works like bags and multisets in other languages.
I've adapted it for Python2.5/2.6 so people can start using it right
away:
http://docs.python.org/dev/library/collections.html#counter-objects
Here's a link to the docs for the new class:
http://code.activestate.com/recipes/576611/
Hi Raymond,
* I'm not a native speaker, but why use the word "Counter"? A "counter"
to my ear sounds like a number that is increased each time an event
occurs; the website counter, eg, comes to mind. I can understanda its
meaning probably stretches to "an object that counts", but I really can't
think of it as a group of object, or a container of object. Moreover, I
find it a much more useful abstraction the idea of a "multi-set" (that
is, a set where elements can appear with multiple cardinality), rather
than stressing the concept of "counting" how many times each element
appears in the set.
* I find it *very* confusing c.items() vs c.elements(). Items and
elements are synonymous (again, in my understanding of English).
I concur and would like to say additionally that having Counter's
len() be the number of *unique* items as opposed to just the number of
items seems a bit counterintuitive.
In fact, I think that it makes sense when you're stressing the fact that
it's just a dictionary of objects and their counters (which the name
"Counter" in fact stresses).
And my main objection is exactly this: a multiset is a differnt abstract
data structure (which is probably worth its own ABC in Python); the fact
that can be implemented through a mapping of objects and counters is
just its concrete implementation. This was perfectly represented by
Raymond's previous bag class, that was *using* a dictionary instead of
*being* a dictionary.
--
Giovanni Bajo
Develer S.r.l.
http://www.develer.com
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