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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def walk(node):
 """ Iterate over all nodes. This is useful if you only want to modify nodes in place and don't care about the context or the order the nodes are returned. """

    from collections import deque
    todo = deque([node])
    while todo:
        node = todo.popleft()
        todo.extend(iter_child_nodes(node))
        yield node