How to convert Json object into tree type in python?

Question

I have the following Json:

 { 
   file1: {
     path_to_file: 'file1.txt',
     children : 'file2'
   },
   file2: {
     path_to_file: 'file1.txt',
     children : 'file3,file4'
   },
   file3: {
     path_to_file: 'a/file3.txt',
     children : ''
   },
   file4: {
     path_to_file: 'b/file4.txt',
     children : ''
   }
 }

I want to construct a tree from this Json. each node should have: name (file1 etc..), path_to_file which is just a data field and convert the children into "pointers" to next node.

I have the following code:

class Node(object):
    def __init__(self, name, path_to_file=None):
        self.name = name
        self.path_to_file= path_to_file
        self.children = []

    def add_child(self, obj):
        self.children.append(obj)

This can be used as:

>>> n = Node(5)
>>> p = Node(6)
>>> q = Node(7)
>>> n.add_child(p)
>>> n.add_child(q)

Now, I want to use properties from my json instead of the number above. So I have this code:

jsonObject= json.load(json_string)
for key in jsonObject:
   value = jsonObject[key]
   print("The key and value are ({}) = ({})".format(key, value))

This gives me:

json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 2 column 4 (char 7)

How can I extract the properties in the Json object inorder to construct the call to the Node class?

You get an error because json_string is likely an invalid JSON. Otherwise, our code looks ok-ish. Also, for key, value in jsonObject.items(): is more idiomatic. — Martin Indra
– Martin Indra, Commented Apr 3, 2019 at 7:45
@MartinIndra When I copy paste this Json example to jsoneditoronline.org it parse it ok. — Luis
– Luis, Commented Apr 3, 2019 at 7:47

sunnky · Accepted Answer · 2019-04-03 09:42:17Z

2

Your json is not a standard json format, it should be double quotes, no single quotes

import json

json_string = """
{
    "file1": {
        "path_to_file": "file1.txt",
        "children": "file2"
    },
    "file2": {
        "path_to_file": "file1.txt",
        "children": "file3,file4"
    },
    "file3": {
        "path_to_file": "a/file3.txt",
        "children": ""
    },
    "file4": {
        "path_to_file": "b/file4.txt",
        "children": ""
    }
}
"""

jsonObject = json.loads(json_string)
for key in jsonObject:
   value = jsonObject[key]
   print("The key and value are ({}) = ({})".format(key, value))

output as:

The key and value are (file1) = ({'path_to_file': 'file1.txt', 'children': 'file2'})
The key and value are (file2) = ({'path_to_file': 'file1.txt', 'children': 'file3,file4'})
The key and value are (file3) = ({'path_to_file': 'a/file3.txt', 'children': ''})
The key and value are (file4) = ({'path_to_file': 'b/file4.txt', 'children': ''})

update answer

For better display, I added the dump method.

import json
json_string = """
{
    "file1": {
        "path_to_file": "file1.txt",
        "children": "file2"
    },
    "file2": {
        "path_to_file": "file1.txt",
        "children": "file3,file4"
    },
    "file3": {
        "path_to_file": "a/file3.txt",
        "children": ""
    },
    "file4": {
        "path_to_file": "b/file4.txt",
        "children": ""
    }
}
"""


class Node(object):
    def __init__(self, name, path_to_file=None):
        self.name = name
        self.path_to_file = path_to_file
        self.children = []

    def add_child(self, obj):
        self.children.append(obj)

    def dump(self, indent=0):
        """dump tree to string"""
        tab = '    '*(indent-1) + ' |- ' if indent > 0 else ''
        print('%s%s' % (tab, self.name))
        for obj in self.children:
            obj.dump(indent + 1)


name2info = json.loads(json_string)


def get_tree(name):
    info = name2info[name]
    root = Node(name, info['path_to_file'])
    for child in info['children'].split(","):
        if child:
            root.add_child(get_tree(child))
    return root


root = get_tree('file1')

# get children info
print(root.name, root.children[0].name, root.children[0].children[1].path_to_file)

root.dump()

it outputs:

file1 file2 b/file4.txt
file1
 |- file2
     |- file3
     |- file4

edited Apr 3, 2019 at 9:42

answered Apr 3, 2019 at 7:47

sunnky

1756 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Luis Over a year ago

Thx. So now I can generate the it as: Node(key,value.get("path_to_file") But I'm not sure how I can return the whole tree type ?

Luis Over a year ago

awesome! Works perfectly. can you explain a bit about the logic?

sunnky Over a year ago

1. Create a node based on the name passed in, 2. If the node has children, initialize it (repeat 1-2) and join the chidren attribute of this node. 3. Finally return the entire node, The whole process is recursive thinking

Luis Over a year ago

The only problem I have with this solution is that you specify root = get_tree('file1') - I need it to be detected from the Json.. The root isn't always the first one.

Collectives™ on Stack Overflow

How to convert Json object into tree type in python?

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related