Kristofer Tengström wrote:
> Thanks everyone, moving the declaration to the class's __init__ method
> did the trick. Now there's just one little problem left. I'm trying to
> create a list that holds the parents for each instance in the
> hierarchy. This is what my code looks like now:
>
> -----------------------------------------
>
> class A:
> def __init__(self, parents=None):
> self.sub = dict()
> if parents:
You should explicitly test for None here; otherwise in a call like
ancestors = []
a = A(anchestors)
the list passed as an argument will not be used, which makes fore confusing
behaviour.
> self.parents = parents
> else:
> self.parents = []
> def sub_add(self, cls):
> hierarchy = self.parents
> hierarchy.append(self)
Here you are adding self to the parents (that should be called ancestors)
and pass it on to cls(...). Then -- because it's non-empty -- it will be
used by the child, too, and you end up with a single parents list.
> obj = cls(hierarchy)
> self.sub[obj.id] = obj
While the minimal fix is to pass a copy
def sub_add(self, cls):
obj = cls(self.parents + [self])
self.sub[obj.id] = obj
I suggest that you modify your node class to keep track only of the direct
parent instead of all ancestors. That makes the implementation more robust
when you move a node to another parent.
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