On 2019-03-22 02:40, Dan Sommers wrote:
On 3/21/19 9:19 PM, Christopher Barker wrote:
https://docs.python.org/3.8/library/collections.html has some
examples using collections.Counter, which is clearly described
as being a subclass of dict. Amongst the examples:
c + d # add two counters together: c[x] + d[x]
That's the + operator operating on two dicts (don't make me
quote the Liskov Substitution Principle), but doing something
really different than the base operator.
So if I know that c and d (or worse, that one of them) is a
dict, then interpreting c + d becomes much more interesting,
Killing a use of a common operator with a very common built in data type
because the operator is used in a different way by a specialized object in
the stdlib seems a bit backwards to me.
Perhaps. Note that Counter also uses | and & for other
operations that probably wouldn't make much sense on base
dicts.
Frankly, I think considering Counter as a dict subclass is the mistake
here, even if it is true.
I had the same thought that Counter is misdesigned in one
way or another, but (a) that ship has long sailed, and (b)
I didn't want to run off on that tangent.
[snip]
Counter is trying to provide the functionality of 2 kinds of container:
1. A counting container.
2. A multi-set.
+ makes sense for counting (sum); | makes sense for multi-sets (union).
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