[Python-ideas] collections.Counter should implement __mul__, __rmul__
Wes Turner
wes.turner at gmail.com
Sun Apr 15 18:45:56 EDT 2018
Good call. Is it any faster to initialize Counter with a dict comprehension?
return Counter({k: v*scalar for (k, v) in self.items())
On Sun, Apr 15, 2018 at 5:05 PM, Peter Norvig <peter at norvig.com> wrote:
> For most types that implement __add__, `x + x` is equal to `2 * x`.
>
> That is true for all numbers, list, tuple, str, timedelta, etc. -- but not
> for collections.Counter. I can add two Counters, but I can't multiply one
> by a scalar. That seems like an oversight.
>
> It would be worthwhile to implement multiplication because, among other
> reasons, Counters are a nice representation for discrete probability
> distributions, for which multiplication is an even more fundamental
> operation than addition.
>
> Here's an implementation:
>
> def __mul__(self, scalar):
> "Multiply each entry by a scalar."
> result = Counter()
> for key in self:
> result[key] = self[key] * scalar
> return result
>
> def __rmul__(self, scalar):
> "Multiply each entry by a scalar."
> result = Counter()
> for key in self:
> result[key] = scalar * self[key]
> return result
>
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> https://mail.python.org/mailman/listinfo/python-ideas
> Code of Conduct: http://python.org/psf/codeofconduct/
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20180415/83819c39/attachment-0001.html>
More information about the Python-ideas
mailing list