Which Python Language Rule Allows The Descriptor To Be Found First?

I bumped into the following last night and I'm still at a loss as to explain it: class Foo(object): @property def dave(self): vars(self)['dave'] = 1 return

Solution 1:

My understanding of attribute access is that the instance dictionary is checked before the class dictionary, and the dictionary of any bases

Data descriptors are an exception:

For instance bindings, the precedence of descriptor invocation depends on the which descriptor methods are defined. Normally, data descriptors define both __get__() and __set__(), while non-data descriptors have just the __get__() method. Data descriptors always override a redefinition in an instance dictionary. In contrast, non-data descriptors can be overridden by instances.

http://docs.python.org/reference/datamodel.html#invoking-descriptors