I like null coalesce too. :)
I know that BDFL has said no to ? Before, but was that for the if-then
shorthand only?
Perhaps submit a new thread to this list so people can discuss/find?
-Joseph
> On Feb 28, 2017, at 10:21 AM, Mark E. Haase <meha...@gmail.com> wrote:
>
> This could be solved with a null-coalescing operator, e.g. PEP-505.
>
> >>> val = conf.get('setting_name') ?? load_from_db('setting_name')
>
> The right side isn't evaluated unless the left side is None. It's similar to
> this:
>
> >>> val = conf.get('setting_name') or load_from_db('setting_name')
>
> Except that using "or" would result in any false-y value (0, "", [], etc.)
> being overridden by the result of `load_from_db(...)`.
>
> I'm not strongly opposed to "lazy", but I think null-coalescing is easier to
> reason about.
>
>
>> On Tue, Feb 28, 2017 at 7:04 AM, Michel Desmoulin
>> <desmoulinmic...@gmail.com> wrote:
>> The debate on the 'lazy' keyword seems to have settled, but I don't know
>> if somebody is trying to write a PEP about it.
>>
>> Anyway, I was doing something like this the other day:
>>
>> conf.get('setting_name', load_from_db('setting_name'))
>>
>> And then realized I could save a query not doing the load_from_db() call
>> most of the time.
>>
>> But dict.get didn't accept callable so I couldn't do:
>>
>> conf.get('setting_name', lambda key: load_from_db('setting_name'))
>>
>> Which is standard practice in a lot of popular Python libs on Pypi.
>>
>> Instead I did:
>>
>> val = conf.get('setting_name')
>> if val is None:
>> val = load_from_db('setting_name')
>>
>> Which is way more verbose. It also has a bug if None is a valid
>> configuration value or if I expect my code to be thread safe.
>>
>> It was not a problem for me, but in that case one would even have to do:
>>
>> try:
>> val = conf['setting_name']
>> except KeyError:
>> val = load_from_db('setting_name')
>>
>> Which is even more verbose.
>>
>> I was going to suggest to python-ideas to update the dict.get()
>> signature to accept a callable, but it would break compatibility with
>> many code actually getting a callable.
>>
>> We could do it for Python 4, but it's far way.
>>
>> 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'))
>>
>>
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