[Python-ideas] PEP: Dict addition and subtraction
steve at pearwood.info
Fri Mar 15 10:59:07 EDT 2019
On Fri, Mar 15, 2019 at 12:25:22PM +0100, Antoine Pitrou wrote:
> Yeah, well.... I do think "+=" for lists was a mistake. I *still* have
> trouble remembering the exact difference between "list +=" and
> "list.extend" (yes, there is one: one accepts more types than the
> other... which one it is, and why, I never remember;
Both accept arbitrary iterables, and the documentation suggests that
they are the same:
Perhaps you are thinking of the difference between list + list versus
list += iterable?
> There is a virtue to
> """There should be one-- and preferably only one --obvious way to do
"It" here refers to two different things:
"I want to update a dict in place":
The Obvious Way is to use the update method; the fact that += works as
well is just a side-effect of the way augmented assignments are defined.
"I want a new dict that merges two existing dicts":
The Obvious Way is to use the merge operator (possibly spelled + but
that's not written in stone yet).
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