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POPython: ambiguities when (un-)pickling a dict-based tree
 

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  1. POPython: ambiguities when (un-)pickling a dict-based tree
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    <p>I have a simple tree structure where each node can have several children which are accessed through keys (+ some payload stored in <code>value</code>):</p> <pre><code>class NodeDict(dict): def __init__(self, parent): self.parent = parent self.value = None def AddChild(self, label): self[label] = NodeDict(self) return self[label] class TreeDict: def __init__(self): self.root = NodeDict(None) def ToString(self, level, node): res = ":" + str(node.value) + "\n" for k, v in node.items(): res += " "*level + str(k) + self.ToString(level + 1, v) return res def __str__(self): return self.ToString(1, self.root) </code></pre> <p>When I try to pickle such a tree I have the problem that it is not correctly unpickled as the following example shows:</p> <pre><code>class Obj: def __init__(self, v): self.v = v def __str__(self): return str(self.v) t = TreeDict() a = t.root.AddChild(Obj("A")) b = a.AddChild(Obj("B")) c = b.AddChild(Obj("C")) d = b.AddChild(Obj("D")) e = a.AddChild(Obj("E")) print t import cPickle cPickle.dump(t, open("test.dat", "w")) t = cPickle.load(open("test.dat", "r")) print t </code></pre> <p>The tree looks like this before</p> <pre><code>:None A:None E:None B:None C:None D:None </code></pre> <p>and like this after pickling and unpickling:</p> <pre><code>:None A:None B:None B:None D:None C:None E:None E:None </code></pre> <p>The problem arises from the fact that I am using <code>Obj</code> as <code>label</code>s in the tree (i.e. as keys in the <code>dict</code>). (It also fails when using e.g. strings instead of <code>Obj</code> if they are not all mutually different.) </p> <p>How could this be changed to work as intended?</p>
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    1. USfuenfundachtzig
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    1. CODo you get the same behaviour if you use the pickle package rather than cpickle?
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      1. USTom Dalton
    2. COCan you make you classes new-style by making TreeDict and Obj inherit from object? Does the behaviour change?
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      1. POPython: ambiguities when (un-)pickling a dict-based tree
      1. USTom Dalton
    3. CO`pickle` fails already on saving (maybe rightfully...)
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      1. USfuenfundachtzig
 

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