How to get nested elements from a JSON Object?

February 22, 2022

JSON file I have has following data:

{
    "P1":{
        "L1":{
            "crn":"1"
        },
        "L2":{
            "crn":"100"
        }
        
    },
    "P2":{
        "L3":{
            "crn":"xx"
        },
        "L4":{
            "crn":"xxxx"
        }
    }
}

How do I get [L1,L2,L3,L4] efficiently?
I can load the data and loop over dict.values().

Is there any better, efficient way?

>Solution :

You can use a list comprehension to extract the room numbers, then use itertools.chain.from_iterable to flatten everything into a one-dimensional list:

import json
from itertools import chain

with open('input.json') as input_file:
    data = json.load(input_file)
    # Prints ['L1', 'L2', 'L3', 'L4']
    print(list(chain.from_iterable(value.keys() for value in data.values())))