On Sep 5, 3:43 pm, Peter Otten <__pete...@web.de> wrote: > 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.
I may not be understanding the OP correctly, but going by what you've put here, I might be tempted to take this kind of stuff out of the class's and using a graph library (such as networkx) - that way if traversal is necessary, it might be a lot easier. But once again, I must say I'm not 100% sure what the OP wants to achieve... Jon. -- http://mail.python.org/mailman/listinfo/python-list
