Build a tree in python through recursion by taking in json object

Question

i'm new to python and i have to build a tree in python after taking in input from a text file
i have the below data in a text file. I have to build a tree in python with the below data using Json

            {
                "component": "A",
                "status": 0,
                "children": [
                    {
                        "component": "AA",
                        "status": 0,
                        "children": [
                            {
                                "component": "AAA",
                                "status": 0,
                                "children": []
                            },
                            {
                                "component": "AAB",
                                "status": 0,
                                "children": []
                            }
                        ]
                    },
                    {
                        "component": "AB",
                        "status": 0,
                        "children": [
                            {
                                "component": "ABA",
                                "status": 0,
                                "children": []
                            },
                            {
                                "component": "ABB",
                                "status": 0,
                                "children": []
                            }
                        ]
                    }
            }

i wrote the below code but it has syntax errors which Im unable to correct if any one can find them

            class node:
                #Construction of Node with component,status and children
                def _init_(self,component=None,status=None,children=None):
                    self.component = component
                    self.status = status
                    if children is None:
                        self.children = [] 
                    else:
                        self.children = children

            #Building Json object from text file            
            class start:
                import json

                f=open("json_file.txt")
                data=json.load(f)
                buildnode(data)


            #Construction of tree through recursion            
            class implementation:
                def buildnode(self,ob):
                    node1= node()
                    node1.component=ob.component
                    node1.status=ob.status
                    node1.children=[]
                    print 'component',component,'','status',status
                    for children in ob:
                        node1.children.add(buildnode(children[i])) 

                    return node1

The error I'm seeing is a decoding error related to the JSON (it looks like you are missing a closing square bracket on the second to last line) — Jason Sperske
– Jason Sperske, Commented Mar 4, 2013 at 7:26
And the use of a class without invoking an instance of it to call it's buildnode method — Jason Sperske
– Jason Sperske, Commented Mar 4, 2013 at 7:29

root · Accepted Answer · 2013-03-04 10:55:35Z

6

import json

class Node(object):
    def __init__(self, component=None, status=None, level=0):
        self.component = component
        self.status    = status
        self.level     = level
        self.children  = []

    def __repr__(self):        
        return '\n{indent}Node({component},{status},{children})'.format(
                                         indent = self.level*'\t', 
                                         component = self.component,
                                         status = self.status,
                                         children = repr(self.children))
    def add_child(self, child):
        self.children.append(child)    

def tree_builder(obj, level=0):
    node = Node(component=obj['component'], status=obj['status'], level=level)
    for child in obj.get('children',[]):
        node.add_child(tree_builder(child, level=level+1))
    return node

def load_json(filename):
    with open(filename) as f:
        return json.load(f)

obj = load_json('test.json')
tree = tree_builder(obj)
print tree

Output:

Node(A,0,[
    Node(AA,0,[
        Node(AAA,0,[]), 
        Node(AAB,0,[])]), 
    Node(AB,0,[
        Node(ABA,0,[]), 
        Node(ABB,0,[])])])

edited Mar 4, 2013 at 10:55

answered Mar 4, 2013 at 10:06

root

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2 Comments

Jason Sperske Over a year ago

+1 for getting the depth code in there and for cleaner class design

Praneeth Over a year ago

My mentor is really pleased seeing this .... i told him i wrote this on my own :P thanks

Jason Sperske · Accepted Answer · 2013-03-04 07:37:17Z

2

Ok I was able to fix the bugs in your code and now it looks like this:

class node:
    #Construction of Node with component,status and children
    def _init_(self,component=None,status=None,children=None):
        self.component = component
        self.status = status
        if children is None:
            self.children = [] 
        else:
            self.children = children

#Construction of tree through recursion            
class implementation:
    def buildnode(self,ob):
        node1= node()
        node1.component=ob['component']
        node1.status=ob['status']
        node1.children=[]
        print 'component',node1.component,'','status',node1.status
        for children in ob['children']:
            node1.children.append(self.buildnode(children)) 

        return node1

#Building Json object from text file            
class start:
    import json

    f=open("json_file.txt")
    data=json.load(f)
    builder = implementation()
    builder.buildnode(data)

This produces the following output:

component A  status 0
component AA  status 0
component AAA  status 0
component AAB  status 0
component AB  status 0
component ABA  status 0
component ABB  status 0

Here is some explanation for what was needed:

First you are calling your buildnode() before you define it, and it is a class function so you need an instance of the class before you call it. Next when you are calling for values inside a dictionary you need to access them by dictionary['key']. The only other big thing was the way to append to an array is to call .append() and not .add().

answered Mar 4, 2013 at 7:37

Jason Sperske

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4 Comments

Praneeth Over a year ago

Thanks a lot Jason . Can't believe it actually worked, u solved all the issues which even my mentor couldn't catch ... thanks :D

Jason Sperske Over a year ago

Was your mentor voting on this answer :P Glad I could help :) I'm enjoying learning Python as well

root Over a year ago

Although you have fixed the syntax errors, this is almost a perfect example of the many things you shouldn't do: two classes, that shouldn't be classes, violating python naming conventions, not closing a file after opening it, etc...

Jason Sperske Over a year ago

@root, all valid points and you have my up vote. This is something I really love about StackOverflow, a good enough answer is often superseded with an even better one :)

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