En Fri, 04 Apr 2008 00:41:19 -0300, Alex VanderWoude <[EMAIL PROTECTED]> escribió:
> Consider the following module: > > ================================ > class NewDict(dict): > parent = None > > def __setitem__(self, key, value): > print "My parent is", self.parent > super(NewDict, self).__setitem__(key, value) > > class Zero(object): > children = NewDict() > > def __init__(self): > self.children.parent = self > > class One(Zero): > pass > > class Two(One): > pass > > a = One() > a.children["spam"] = "baked beans" > b = Two() > b.children["eggs"] = "bacon" > ================================ > > When the above module is executed, the output looks something like this: > > My parent is <__main__.One object at 0x00BA27B0> > My parent is <__main__.Two object at 0x00B9D170> > > ...which is great, just what I wanted. Each dictionary instance reports > correctly which object instance is its container. But only if you create a single instance of each class, because "children" is a class attribute (behaves as it were shared among all instances). Then you need an instance attribute, initialized in __init__. So why not set the parent at this time? py> class NewDict(dict): pass ... py> class Zero(object): ... def __init__(self): ... self.children = NewDict() ... self.children.parent = self ... py> class One(Zero): ... pass ... py> class Two(One): ... pass ... py> a = One() py> a.children["spam"] = "baked beans" py> b = Two() py> b.children["eggs"] = "bacon" py> c = Two() py> c.children["foo"] = "bar" py> print a.children.parent is a True py> print b.children.parent is b True py> print c.children.parent is c True > However, I would like to find some automagic way of having NewDict > figure out what object instance it is on without resorting to having the > container class instance poke a reference to itself into the NewDict > instance (i.e. the line in Zero.__init__()). Unless there are more contrains that you haven't told us, the above example looks as the simplest approach. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
