[Python-ideas] Another use case for the 'lazy' (aka 'delayed') keyword

[Michel Desmoulin]

Le 28/02/2017 à 13:19, Chris Angelico a écrit :
> On Tue, Feb 28, 2017 at 11:04 PM, Michel Desmoulin
> <desmoulinmichel at gmail.com> wrote:
>> Instead, I think it's a good example of were 'lazy' could help. You
>> can't get simpler than:
>>
>> conf.get('setting_name', lazy load_from_db('setting_name'))
>>
> 
> Alternatively, you could define 'conf' as a subclass of dict with a
> __missing__ method:
> 
> class Config(dict):
>     def __missing__(self, key):
>         self[key] = load_from_db(key)
>         return self[key]
> conf = Config()
> 
> Then it becomes even simpler AND less redundant:
> 
> conf['setting_name']

Yes but this assumes:

- I have access to the code instantiating conf;
- all code using conf are using load_from_db as a default value;
- load_from_db exists for all code using the conf object

There is always a solution to all problems, as Python is turing complete.

You don't need list comprehension, you can use a for loop.

You don't need upacking you can uses indexing.

And you don't need lazy, it's just convenient.