Does ZODB have something equivalent to Durus' Computed Attributes? Which I understand are attributes (or methods) on a Persistent object that compute a value from some other attributes and then cache that result for each connection, and if any of the attributes from which the Computed Attribute computes its result change, the new result will be automatically computed and all connections will have their cached value invalidated.
Zope 2 has ComputedAttribute. It allows you to access the result of a method as an attribute:
from ComputedAttribute import ComputedAttribute import ExtensionClass
class Example(ExtensionClass.Base):
def _anAttribute(self):
return 'foo'anAttribute = ComputedAttribute(_anAttribute)
>>> example = Example() >>> example.anAttribute 'foo' >>>
On a related note, do properties work with Persistent objects in ZODB? I mean the Python property() function. I do not know how it interacts with __getattr__() and stuff, and I know the ZODB docs warn against messing with those functions for Persistent classes. If they do work, do they basically serve as a non-cached computed attribute? Is a Durus Computed Attribute just a property with caching and consistency for multiple connections? (I know this isn't a Durus list.)
For your information:
property() doesn't work for ExtensionClass bases classes. You can't use them in Zope 2 up to 2.7. Python properties are working with ZODB 3.3+ (Zope 2.8 and Zope3).
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