That's actually how I coded it myself the first time. But I worried it would be wasteful to create an intermediate dict and discard it.

`timeit` results: 3.79 µs for the for-loop, 5.08 µs for the dict-comprehension with a 10-key Counter 257 µs for the for-loop, 169 µs for the dict-comprehension with a 1000-key Counter So results are mixed, but you are probably right. On Sun, Apr 15, 2018 at 3:46 PM Wes Turner <wes.tur...@gmail.com> wrote: > 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 <pe...@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@python.org >> https://mail.python.org/mailman/listinfo/python-ideas >> Code of Conduct: http://python.org/psf/codeofconduct/ >> >> >

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