Modified Preorder Tree Traversal to Python structure

Question

Hi I am trying to represent a Modified-Preorder-Tree-Traversal as a Python structure I can then output to json as my current goal is to display the tree in jstree

Lets say I have a table as shown http://imrannazar.com/Modified-Preorder-Tree-Traversal (Each row also has a parent_id in my case) like so

    Node ID   Name       Left MPTT value     Right MPTT value       ParentID
     1       (Root)             1                 16                   -1
     2       Articles           2                 11                    1
     5       Fiction            3                 8                     2
     7       Fantasy            4                 5                     5
     8       Sci-fi             6                 7                     5
     6       Reference          9                 10                    2
     3       Portfolio          12                13                    1
     4       Contact            14                15                    1

The Json format for jstree is like

    [
      {
       "data" : "Root",
       "children" : [ 
           {
              "data":"Articles",
               "children : [
                             {"data":"Fiction"},
                             {"data":"Reference"}
                            ]
           },
           {"data":"Portfolio"},
           {"data":"Contact"}]
      },
    ]

How can I convert the above table to a Python format to output this json.

I thought about somehow using a nested dictionary as below

    class NestedDict(dict):
        def __missing__(self, key):
            return self.setdefault(key, NestedDict())

Not sure of the algorithm I need though.

Any help greatly appreciated.

Thanks

Answer 1

You should really try to do it yourself, show what you've done and where it doesn't work. But I had a few minutes free, so...

To parse the table, you can use the csv module. I'll leave that to you.

Probably not an optimal solution, but this will do it:

datain = (
    (1,'Root',1,16,-1),
    (2,'Articles',2,11,1),
    (5,'Fiction',3,8,2),
    (7,'Fantasy',4,5,5),
    (8,'Sci-fi',6,7,5),
    (6,'Reference',9,10,2),
    (3,'Portfolio',12,13,1),
    (4,'Contact',14,15,1),
    )

def convert_to_json(data):
    node_index = dict()
    parent_index = dict()
    for node in data:
        node_index[node[0]] = node
        parent_index.setdefault(node[4],[]).append(node)

    def process_node(index):
        result = { 'data' : node_index[index][1] }
        for node in parent_index.get(index,[]):
            result.setdefault('children',[]).append(process_node(node[0]))
        return result

    node = process_node(1)
    return [node]

Returns:

[
    {
        'data': 'Root',
        'children': [
            {
                'data': 'Articles',
                'children': [
                    {
                        'data': 'Fiction',
                        'children': [
                            { 'data': 'Fantasy' },
                            { 'data': 'Sci-fi' }
                            ]
                    },
                    { 'data': 'Reference' }
                ]
            }, 
            { 'data': 'Portfolio' },
            { 'data': 'Contact' }
        ]
    }
]