On 2017-02-28 12:04, Michel Desmoulin 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.
[snip]
If None is a valid value, then use a sentinel:
MISSING = object()
val = conf.get('setting_name', MISSING)
if val is MISSING:
val = load_from_db('setting_name')
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