Static caching property

[Ethan Furman]

On 03/21/2016 10:03 AM, Joseph L. Casale wrote:

>> One solution is to use descriptor protocol on the class, which means
>> using a metaclass. I'm not sure it's the best option, but it is an
>> option.
>
> I will look at that, I wonder if however I am not over complicating it:
>
> class Foo:
>      _bar = None
>      @property
>      def expensive(self):
>          if Foo._bar is None:
>              import something
>              Foo._bar = something.expensive()
>          return Foo._bar
>
> Somewhat naive, but a test with if is pretty cheap...

A slightly cleaner approach (but only slightly):

   class Cache(object):
       _sentinal = object()
       def __init__(self, expensive_func):
           self.value = self._sentinal
           self.func = expensive_func
       def __get__(self, *args):
           if self.value is self._sentinal:
               self.value = self.func()
          return self.func()

The advantages:

- only one location in the class
- works correctly whether accessed via class or instance
- clue as to functionality in the name

--
~Ethan~