On Thu, Sep 15, 2016 at 4:40 AM, monik...@netzero.net <monik...@netzero.net> wrote: > class GetSet(): > > def __init__(self, value): > self.attrval = value > > @property > def var(self): > print "getting the var attribute" > return self.attrval > @var.setter > def var(self,value): > print "setting the var attribute" > self.attrval = value > > @var.deleter > def var(self): > print "deleting the var attribute" > self.attrval = None > > me = GetSet(5) > me.var = 1000
A classic instance has both a type (`instance`) and a __class__ (e.g. GetSet). The type defines how getting, setting, and deleting attributes works, and the hard-coded classic behavior for calling the class __getattr__, __setattr__, and __delattr__ methods. If the class doesn't define __setattr__ and __delattr__, the instance type sets and deletes attributes directly in the instance dict. Unlike new-style classes, a data descriptor defined by the class gets ignored here. Getting attributes also prefers the instance dict. However, to support bound methods (e.g. __init__), it falls back on a class lookup and calls the descriptor __get__ method if defined. Unintentionally, it happens that this partially supports the property descriptor. But since there's no data descriptor support, it's only useful for read-only properties. _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
