On Mon, Jul 25, 2011 at 11:46 AM, Jack Bates <ms...@freezone.co.uk> wrote:
> How can you get a descriptor to return an identical value, each time
> it's called with the same "instance" - without leaking memory?
class MyDescriptor(object):
def __get__(self, instance, owner):
try:
return instance.__cached_value[self]
except AttributeError:
instance.__cached_value = {self: get_value(instance, owner)}
except KeyError:
instance.__cached_value[self] = get_value(instance, owner)
return instance.__cached_value
class MyClass(object):
my_attribute = MyDescriptor()
Placing the cache on the object instance ensures that it won't outlive
the object, and since the full attribute name will be
_MyDescriptor__cached_value, it's highly unlikely to conflict with an
existing attribute. Keying the value on self is necessary in case the
object has multiple descriptors of the same type.
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