Counter Class -- Bag/Multiset

[MRAB]

Terry Reedy wrote:
> bearophileHUGS at lycos.com wrote:
> 
>> Also: what's the rationale of allowing negative values too?
> 
> I can guess two:
> 1) Nuisance to check given that Python does not have a count
> (0,1,2...) type.
> 2. Useful. + = items on hand; - = items back-ordered. Bank account go
> negative also ;-). So does elevation.
> Similarly, an app could set 0 to mean 'desired quantity on hand', so
> non-zero count is surplus or deficit.
> 
> I might not have thought to allow this, but it seems to open new 
> applications.  (This definitely makes bag or multiset inappropriate
> as names.)
> 
I would've limited the counts to non-negative values too, but being able
to store negative values does allow credit/debit or in-stock/on-order.
In such cases, the name 'Counter' makes more sense.