[Python-Dev] collections module
aleaxit at yahoo.com
Fri Jan 9 10:56:40 EST 2004
On Friday 09 January 2004 04:20 pm, Skip Montanaro wrote:
> Raymond> I would like to establish a new module for some collection
> Raymond> classes.
> Raymond> The first type would be a bag, modeled after one of
> Smalltalk's Raymond> key collection classes (similar to MultiSets in C++
> and bags in Raymond> Objective C).
> I'm neither a Smalltalk, C++ or Objective C programmer. How is a bag
> different from a set?
In a bag, or multiset, a certain item can be in the collection a given
_number_ of times, rather than just "either being there or not" as in a set.
> In my GE days (pre-Python) we had a collection class
> in a proprietary language which was used as a proxy. You'd send a message
> to the collection and it would forward it to all the elements it contained.
> This was rather convenient. You could tell all the actors to turn and face
> the camera, for example.
> Oddly enough, although we used collections heavily, I never really missed
> that functionality in Python. I implemented it once or twice, but never
> used it much. Different style of programming I guess.
Yes, there are "proxying-containers" like that in the Python Cookbook, too --
and I've noticed I also don't use them. "for item in collection: item.turn()"
is just too nice and general an idiom (with the per-item processing being
expressible inline, which is often a big clarity win in Python) to easily
yield to replacement by collection.each(lambda x: x.turn()) or the like...
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