Question

I have some code that does some manipulation of classes. The details aren’t terribly important. headerDict is a dictionary that contains lists of objects from the class NodeCluster. Node1 and Node2 are objects from the class NodeCluster. .header is an attribute of the NodeCluster class. What I want to do is iterate over the class objects in the node2 entry of headerDict, change their header attributes, and — here’s the problem part — append each class object to a list in node1’s headerDict. Here’s a code snippet:

if len(headerDict[node1.header]) >= len(headerDict[node2.header]):
        for node in headerDict[node2.header]:
            node.k = node.k - 1
            node.header = node1.header
            headerDict[node1].append(node)

However, when I try to perform the append operation, I get this error:

KeyError: <__main__.NodeCluster instance at 0x10047b050>

What gives?

Answer 1

I suspect the following will fix it:

        headerDict[node1.header].append(node)
                        ^^^^^^^

since everywhere else you’re using .header to index into headerDict.