Generic way to get the value of key in nested json using python

Question

I was new to python, my requirement is to check whether the given key exists on the json or not. Json will not be same all the time. So, am looking for the generic function to check whether the key exists. It works for simple json , but returns nothing when the json itself has another json with an jsonarray inside as shown below:

{
  "id": "1888741f-173a-4366-9fa0-a156d8734972",
  "type": "events",
  "version": "1.0.0",
  "count": 3,
  "payload": {
    "cmevents": [
      {
        "exit_code": "0dbc2745-a964-4ce3-b7a0-bd5295afc620",
        "sourceEventType": "test01",
        "sourceType": "test",
        product:{
        "productCode":"101"
        }
      },
      {
        "exit_code": "1dbc2745-a964-4ce3-b7a0-bd5295afc620",
        "sourceEventType": "test02",
        "sourceType": "test",
        product:{
        "productCode":"102"
        }
      },
      {
        "exit_code": "2dbc2745-a964-4ce3-b7a0-bd5295afc620",
        "sourceEventType": "test03",
        "sourceType": "test",
        product:{
        "productCode":"103"
        }
      }
    ]
  }
}

from the above json , i wants to check the key sourceEventType exists in all items of cmevents list. Following is the function I have used

def checkElementsExist(element, JSON, path, whole_path):
    if element in JSON:
        path = path + element + ' = ' + JSON[element].encode('utf-8')
        whole_path.append(path)
        //
    for key in JSON:
        if isinstance(JSON[key], dict):
            finds(element, JSON[key], path + key + '.', whole_path)

To call the function:

whole_path = []
finds('sourceEventType', json, '', whole_path)

Can anyone please help me with the right solution

For starters this isn't valid json. the product keys need quotes around them. — nlta
– nlta, Commented Oct 11, 2021 at 6:56
"Can anyone please help me with the right solution" Please see meta.stackoverflow.com/questions/284236/… . What actually do you think is the difficulty with fixing the problem yourself? What is your analysis of why the code is malfunctioning, and what question do you have about that behaviour? What were the results of your attempts to debug the code (as is expected of askers)? — Karl Knechtel
– Karl Knechtel, Commented Oct 11, 2021 at 7:06

nlta · Accepted Answer · 2021-10-11 07:02:17Z

1

A recursive function is probably an easier approach here.

Parse the json using json.loads(text)
Search the tree

import json
text = json.loads(".....")
def search_for_key(key, content) -> bool:
    # Search each item of the list
    # if found return true
    if isinstance(content, list):
        for elem in content:
            if search_for_key(key, elem):
                return True
    # Search each key of the dictionary for match
    # If the key isn't a match try searching the value
    # of the key in the dictionary
    elif isinstance(content, dict):
        for key_in_json in content:
            if key_in_json == key:
                return True
            if search_for_key(key, content[key_in_json]):
                return True
    # If here it's a number or string. There is no where else to go
    # return false
    else:
        return False
print(search_for_key("some_key?", text))

It's definitely possible to make your path approach work BUT you're doing need to keep track of what paths you haven't explored yet using a stack/queue (and you get this for free with a recursive function).

answered Oct 11, 2021 at 7:02

nlta

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2 Comments

kaviya .P Over a year ago

There might be a possibilities that we may have the same key exists in parent json object also right.. how can we handle it here?

nlta Over a year ago

@kaviya.P can you show me a test case this fails that you expect to succeed? Not sure what you mean.

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