27.02.19 20:48, Guido van Rossum пише:
On Wed, Feb 27, 2019 at 10:42 AM Michael Selik <mike@selik.org mailto:mike@selik.org> wrote > The dict subclass collections.Counter overrides the update method for adding values instead of overwriting values.
https://docs.python.org/3/library/collections.html#collections.Counter.update Counter also uses +/__add__ for a similar behavior. >>> c = Counter(a=3, b=1) >>> d = Counter(a=1, b=2) >>> c + d # add two counters together: c[x] + d[x] Counter({'a': 4, 'b': 3}) At first I worried that changing base dict would cause confusion for the subclass, but Counter seems to share the idea that update and + are synonyms.Great, this sounds like a good argument for + over |. The other argument is that | for sets *is* symmetrical, while + is used for other collections where it's not symmetrical. So it sounds like + is a winner here.
Counter uses + for a *different* behavior!
Counter(a=2) + Counter(a=3)
Counter({'a': 5})
I do not understand why we discuss a new syntax for dict merging if we already have a syntax for dict merging: {**d1, **d2} (which works with *all* mappings). Is not this contradicts the Zen?