I am trying to write a generic DataAttribute class in order to simplify access to object attributes and attached attribute-metadata for end users with little programming experience.
Requirement 1: accessing the "default" value should be easy (using assignment operator, via descriptors like __get__ and __set__). Requirement 2: access to the attribute-metadata should also be as intuitive as possible. Requirement 3: possibly the DataAttribute should also be callable, to return for instance, an history of its values. class DataAttribute(object): value=1 #default old=2 .... class Obj(object): attr=DataAttribute() #From end user prospective, ideally: obj=Obj() x = obj.attr #x=1 xold = obj.attr.old #xold=2 obj.attr = 3 #obj.attr.value=3 xold = obj.attr.old #xold=1 xhistory = obj.attr(startdate, enddate) #xhistory = [[date1, 4],[date2,5],[date3,6]] xtimestmap = x.attr.timestamp print obj.attr == obj.attr.value #True If I use __get__ then I cannot access the metadata. I could create a separate Obj attribute for each metadata item, but then I would litter the Obj namespace (typical object will have several attributes each with lots of metadata) and potentially create name conflicts. Not to mention that DataAttributes should be attached/deleted on the fly and if each attribute becames a set of attributes this operation is complex (metclasses?). If I use __call__ + __set__ but then I am introducing an asymmetry: x = obj.attr() obj.attr = 2 I could use getters and setters but that is not really convenient nor intuitive -- http://mail.python.org/mailman/listinfo/python-list
