[Python-ideas] collections.Counter multiplication

[Steven D'Aprano]

On 30/05/13 10:52, Matthew Ruffalo wrote:
> On 05/29/2013 08:06 PM, Steven D'Aprano wrote:
>> On 30/05/13 06:17, James K wrote:
>>> It should work like this
>>>
>>>      >>> from collections import Counter
>>>      >>> Counter({'a': 1, 'b': 2}) * 2 # scalar
>>>      Counter({'b': 4, 'a': 2})
>>
>> Under what circumstances would you do this?
>>
>> What is it about Counters that they should support multiplication when no other mapping type does?
>
> Counters are different from other mapping types because they provide a natural Python stdlib implementation of multisets -- the docs explicitly state that "The Counter class is similar to bags or multisets in other languages.". The class already has behavior that is different from other mapping types: Counter.__init__ can also take an iterable of hashable objects instead of another mapping, and Counter.update adds counts instead of replacing them.


None of this answers my question. Under what circumstances would you multiply a counter by a scalar (let alone by another counter)? The fact that counters differ in some ways from other mappings doesn't justify every arbitrary change proposed.




-- 
Steven