Hello,
2017-06-04 Nathaniel Smith <n...@pobox.com> dixit:
> class LazyConstants:
> def __getattr__(self, name):
> value = compute_value_for(name)
> setattr(self, name, value)
> return value
>
> __getattr__ is only called as a fallback, so by setting the computed
> value on the object we make any future attribute lookups just as cheap
> as they would be otherwise.
Another solution is to use a Pyramid's-@reify-like decorator to
make a caching non-data descriptor (i.e., the kind of descriptor that
can be shadowed with an ordinary instance attribute):
```
class LazyConstants:
@reify
def FOO(self):
return <complicated computation...>
@reify
def BAR(self):
return <another complicated computation...>
```
In my work we use just @pyramid.decorator.reify [1], but the mechanism
is so simple that it you can always implement it by yourself [2],
though providing some features related to_ _doc__/introspection-ability
etc. may need some additional deliberation to do it right...
That may mean to it would be worth to add it to the standard library.
Wouldn't be?
Cheers.
*j
[1] See:
http://docs.pylonsproject.org/projects/pyramid/en/latest/api/decorator.html#pyramid.decorator.reify
[2] The gist of the implementation is just:
```
class lazyproperty(object):
def __init__(self, maker):
self.maker = maker
def __get__(self, instance, owner):
if instance is None:
return self
value = self.maker(instance)
setattr(instance, self.maker.__name__, value)
return value
```
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