[New-bugs-announce] [issue40764] Conflation of Counter with Multiset

[Paul]

New submission from Paul <python at paulkoppen.com>:

The collections docs state: "Several mathematical operations are provided for combining Counter objects to produce multisets (counters that have counts greater than zero)."

I am surprised at the clear level of decision into conflating counters with multisets. Why break all functionality for negative counts in favour of multisets? Why not create a Multiset object for multisets?

One example use of negative counts is in factorisation (https://bugs.python.org/msg368298 will be surprised counters don't count)
18   = 2**1 * 3**2  --> x18 = Counter({2: 1, 3: 2})
 4   = 2**2         --> x4 = Counter({2: 2})

To compute 18/4 in this representation (which I believe is exactly precisely a count), one would expect

18/4 = 2**-1 * 3**2 --> x4_5 = x18 - x4 = Counter({2: -1, 3: 2})

But instead,

x18 - x4 = Counter({3: 2}) = 9 ???

This is just an example. The use case for negative counts is plain and obvious. The question is: why does collections break counter behaviour in favour of conflation with multisets? Why not have two objects: Counter for counters and Multiset for multisets?

----------
components: Library (Lib)
messages: 369867
nosy: wpk-
priority: normal
severity: normal
status: open
title: Conflation of Counter with Multiset
type: behavior
versions: Python 3.10, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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<https://bugs.python.org/issue40764>
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