Tree traversal with page property sortIndex

I'm building a tree structure based on a list retrieved from a db.Model called Pages.

Each Page entry has a parentKey property that's a db.SelfReferenceProperty() and a db.IntegerProperty() called sortIndex.

I fetch the list and call a method to travers over the list and make a nestled dict as my tree. The reason I fetch the entire list is that I want to skip multiple queries.

pages = Pages.gql('ORDER BY sortIndex').fetch(1000)
build_tree(pages)

And the build_tree:

def build_tree(nodes, *args):
    # create empty tree to fill
    tree = {}
    build_tree_recursive(tree, None, nodes, *args)

    return tree

def build_tree_recursive(tree, parent, nodes, *args):
    # find root children, first level nodes have no parentKey
    if parent is None:
        children  = [n for n in nodes if n.parentKey == None]
    # find children
    else:
        children  = [n for n in nodes if n.parentKey is not None and n.parentKey.key() == parent]

    # build a subtree for each child
    for child in children:
        # start new subtree
        key = child.key()
        # Use page entry key as unique dict key
        tree[key] = { 'page' : child, 'children' : {}}
        # call recursively to build a subtree for current node
        build_tree_recursive(tree[key]['children'], key, nodes)

The problem is that the list get's rearranged and don't follow det ORDER BY. I think this is due to that each Page is put in the list when a proper parent is found. But even the first level (Pages that has parentKey == None) get's returned in the wrong order.

I've tried setting a prefix using a loop counter on tree[str(i) + '_' + str(key)] but still didn't return in a proper order.

So the question how to get them in an proper order?

EDIT [Solved]:

To preserve the order of the list sent as a param to build_tree I moved to a different angle. I use list instead and the order stays the same:

def build_tree(nodes, *args):
    # create empty tree to fill
    t = {}
    # First group all pages w/ same parent
    for node in nodes:
        if node.parentKey is None:
            key = 'root'
        else:
            key = node.parentKey.key()

        if not t.has_key(key):
            t[key] = []

        t[key].append({ 'page' : node, 'children' : []})

    pageTree = t['root']
    # Iterate over there
    build_page_tree(pageTree, t)

    return pageTree

def build_page_tree(pageTree, nodes):
    #Loop over selected list
    for parent, node in nodes.iteritems():
        # We don't need to loop over first level node
        if parent is not 'root':
            # Loop over current level in page tree
            for item in pageTree:
                # Match keys
                if item['page'].key() == parent:
                    # Save node as child
                    item['children'] = node
                    # Only need to loop over childs if they are present
                    build_page_tree(item['children'], nodes)

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Tree traversal with page property sortIndex

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