[Python-ideas] Add dict.append and dict.extend

[MRAB]

On 2018-06-05 01:25, Steven D'Aprano wrote:
> On Mon, Jun 04, 2018 at 02:22:29PM -0700, Ben Rudiak-Gould wrote:
>> I'd like to propose adding `append` and `extend` methods to dicts
>> which behave like `__setitem__` and `update` respectively, except that
>> they raise an exception (KeyError?) instead of overwriting preexisting
>> entries.
>> 
>> Very often I expect that the key I'm adding to a dict isn't already in
>> it. 
> 
[snip]
>> If I want to verify that, I have to expand my single-line
>> assignment statement to 3-5 lines (depending on whether the dict and
>> key are expressions that I now need to assign to local variables).
> 
> I'm sorry, I can't visualise how it would take you up to five lines to
> check and update a key. It shouldn't take more than two:
> 
> if key not in d:
>      d[key] = value
> 
It shouldn't take more than one:

d.setdefault(key, value)

:-)

[snip]