how to access json data(object) in python

I am not sure whether you want to add the total_points into the last_transaction['points'] or you want to add another "field" called total_points to the last_transaction. This code does both -

if isinstance(json_obj['specific_wallet_transactions'][-1], dict):
    json_obj['specific_wallet_transactions'][-1]['points'] += json_obj['total_points']
    json_obj['specific_wallet_transactions'][-1]['total_points'] = json_obj['total_points']

I'm presuming that you want to sum the points values contained in the specific_wallet_transactions list.

# Check 'specific_wallet_transactions' is a list
if isinstance(o['specific_wallet_transactions'], list):
    # Get the last transaction
    last_transaction = o['specific_wallet_transactions'][-1]
    # Check 'last_transaction' is a dictionary 
    if isinstance(last_transaction, dict):
        # Calculate 'total_points' by calculating the sum of 'points' values
        last_transaction['total_points'] = sum([t['points'] for t in o['specific_wallet_transactions']
                                               if t['points'] is not None])

Complete code:

o = {
    "id": 6,
    "issuer_id": 1,
    "total_points": 100,
    "membership_details": {
        "id": 367,
        "valid_from": "2022-07-26T15:23:43.000+05:30",
        "valid_through": "2023-07-26T15:23:43.000+05:30"
    },
    "specific_wallet_transactions": [
        {
            "id": 9,
            "transaction_type": "Earn",
            "points": 100,
            "points_validity": "2022-04-23T00:00:00.000+05:30",
            "order_meta_data": {},
            "reason_code": "Earn",
            "created_at": "2021-04-23T10:12:41.000+05:30",
            "transaction_name": "Earn"
        },
        {
            "id": 16,
            "transaction_type": "Burn",
            "points": 5,
            "points_validity": "null",
            "order_meta_data": {
                "order_id": "12",
                "given_wallet_ids": [
                    6
                ],
                "used_wallet_ids": [
                    6
                ],
                "burn_type": "pool burn"
            },
            "reason_code": "Burn",
            "created_at": "2021-04-29T16:28:11.000+05:30",
            "transaction_name": "Burn"
        },
        {
            "id": 2775,
            "transaction_type": "Burn",
            "points": 100,
            "points_validity": "null",
            "order_meta_data": {},
            "reason_code": "Expired Points Transaction",
            "created_at": "2022-05-10T17:02:04.000+05:30",
            "transaction_name": "Expire"
        },
        {
            "id": 3654,
            "transaction_type": "Earn",
            "points": 100,
            "points_validity": "2024-07-25T00:00:00.000+05:30",
            "order_meta_data": {},
            "reason_code": "Earn",
            "created_at": "2022-07-26T15:23:42.000+05:30",
            "transaction_name": "Earn"
        }
    ],
    "customer_id": 9,
    "customer_email": "",
    "issuer_name": "The qq",
    "default_currency": "INR",
    "conversion_rate": 1.0,
    "points_monetary_value": 100.0,
    "user_name": "null",
    "segment_code": "ww"
}
 
if isinstance(o['specific_wallet_transactions'], list):
    last_transaction = o['specific_wallet_transactions'][-1]
    if isinstance(last_transaction, dict):
        last_transaction['total_points'] = sum([t['points'] for t in o['specific_wallet_transactions']
                                               if t['points'] is not None])

To view the result:

import json
print(json.dumps(last_transaction, indent=2))

Output:

{
  "id": 3654,
  "transaction_type": "Earn",
  "points": 100,
  "points_validity": "2024-07-25T00:00:00.000+05:30",
  "order_meta_data": {},
  "reason_code": "Earn",
  "created_at": "2022-07-26T15:23:42.000+05:30",
  "transaction_name": "Earn",
  "total_points": 305
}