Get the elements from nested JSON with Python using json lib

Question

I want to list all the elements from "BoxDet" with the "BoxDet" name. The aim is to list it that way: BoxDet : ABC ...

A little part of my JSON:

{
   "id":1,
   "name":"BoxH",
   "readOnly":true,
   "children":[
      {
         "id":100,
         "name":"Box1",
         "readOnly":true,
         "children":[
            {
               "id":1003,
               "name":"Box2",
               "children":[
                  {
                     "id":1019,
                     "name":"BoxDet",
                     "Ids":[
                        "ABC",
                        "ABC2",
                        "DEF2",
                        "DEFHD",
                        "LKK"
                        ]
                    }
                ]
            }
        ]
    }
    ]
}

My problem is just on the beginning, I just cannot go deeper as first { }. My code...

output_json = json.load(open('root.json'))
for first in output_json:
    print first
    for second in first:
        print second

... returns me something like that:

readOnly
r
e
a
d
O
n
l
y
children
c
h
i
l
d
r
e
n

... an so on. I can't really even go deeper to Box1, not even mentioning Box2. I'm working with Python 2.7

Aaron Digulla · Accepted Answer · 2013-09-16 15:05:32Z

10

You need a tree-search algorithm for this:

def locateByName(e,name):
    if e.get('name',None) == name:
        return e

    for child in e.get('children',[]):
        result = locateByName(child,name)
        if result is not None:
            return result

    return None

Now you can use this recursive function to locate the element you want:

node = locateByName(output_json, 'BoxDet')
print node['name'],node['Ids']

answered Sep 16, 2013 at 15:05

Aaron Digulla

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6 Comments

jakkolwiek Over a year ago

Hi Aaron, @Aaron Digulla, another one question. Your solution worked for me as a charm. I'm trying right now to change your code to deliver me in result not the Ids, but the "name" values itself. [pastebin.com/MDPv0PND] this is my json, I want to extract the SUB, SUBSUB and NAME and when using a quasi for-chain, I cound not get back in hierarchy to get the SUBSUB2... Could you please put me somehow on the right track?

Aaron Digulla Over a year ago

Ask a new question, please.

jakkolwiek Over a year ago

Did it [stackoverflow.com/questions/19031797/….

Chielt Over a year ago

@AaronDigulla, why do you need to guard the return result in the for loop? Can't you just return result and leave out the return None at the end?

Aaron Digulla Over a year ago

@Chielt Without the guard, it would only consider the first child.

|

SingleNegationElimination · Accepted Answer · 2013-09-16 14:55:01Z

1

when you try to use a for loop on a dict, without any special consideration, you get only the keys out of the dict. That is:

>>> my_dict = {'foo': 'bar', 'baz':'quux'}
>>> list(my_dict)
['foo', 'baz']
>>> for x in my_dict:
...     print repr(x)    
'foo'
'baz'

The most usual thing to do is to use dict.iteritems() (just dict.items() in python 3)

>>> for x in my_dict.iteritems():
...     print repr(x)
('foo', 'bar')
('baz', 'quux')

Or you can fetch the value for the key yourself:

>>> for x in my_dict:
...     print repr(x), repr(my_dict[x])    
'foo' 'bar'
'baz' 'quux'

answered Sep 16, 2013 at 14:55

SingleNegationElimination

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Comments

Ketouem · Accepted Answer · 2013-09-16 15:02:08Z

1

If you want to iterate through the children of your entities you can do the following:

for children in output_json["children"]:
    #Going down to ID: 100 level
    for grandchildren in children["children"]:
        #Going down to ID: 1003 level
        for grandgrandchildren in grandchildren["children"]:
            #Going down to ID: 1019 level
            if grandgrandchildren["name"] == "BoxDet":
                return "BoxDet" + " ".join(grandgrandchildren["Ids"])

Not that the data structure involved in the json module works more or less like classic dictionary where you access the value through the key:

my_dict[key] = value

edited Sep 16, 2013 at 15:02

answered Sep 16, 2013 at 14:56

Ketouem

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1 Comment

Ketouem Over a year ago

When you use a for-in on a dictionary it iterates on all the key inside the dictionary. "for key in dictionary"

Rafael T · Accepted Answer · 2013-09-16 14:55:19Z

0

try it like this:

output_json = json.load(open('root.json'))
if "children" in output_json:
  children = output_json["children"]
  if "children" in children:
    children1 = children["children"]
    if "children" in children1:
      children2 = children1["children"]
      if "name" in children2:
        name = children2["name"]
      if "Ids" in children2:
        ids = children2["Ids"]
      print name, ids

answered Sep 16, 2013 at 14:55

Rafael T

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