getter and setter and list appends

[Terry Reedy]

dasacc22 wrote:
> Hi,
> 
> I seem to be having a problem with a list being share across multiple
> instantiations of it and dont quite understand why this is happening.

Class attributes are shared by all instances.

> My class looks like this,
> 
> class Widget(object):
>     _parent = None
>     _children = []

Move this line
> 
>     def __init__(self, parent=None):
>         self.parent = parent

to here.
> 
>     @property
>     def children(self):
>         return self._children
> 
>     @property
>     def parent(self):
>         return self._parent
> 
>     @parent.setter
>     def parent(self, obj):
>         if obj:
>             obj._children.append(self)
>             self._parent = obj
> 
> 
> now if i make instances and attach children like so
> 
> a = Widget()
> b = Widget(a)
> c = Widget(a)
> d = Widget(c)
> 
> Basically all the objects end up sharing the _children list from `a`
> instead of forming something like a tree. Any advice would be greatly
> appreciated.
> 
> Thanks,
> Daniel
> --
> http://mail.python.org/mailman/listinfo/python-list
>