How to Append Data to JSON array in Python

In this tutorial, you’ll learn various methods to append data to an existing JSON array in Python.

We’ll cover several examples, from appending to JSON array, appending dictionaries and lists as elements, appending to nested JSON objects, and handling JSON data stored in files.

 

 

Using append()

You can use the append method to append to a JSON array:

import json
feedback_data = [
    {"customer_id": 101, "feedback": "Great coverage"},
    {"customer_id": 102, "feedback": "Fast internet"}
]
new_feedback = {"customer_id": 103, "feedback": "Friendly customer service"}
feedback_data.append(new_feedback)
print(json.dumps(feedback_data, indent=4))

Output:

[
    {
        "customer_id": 101,
        "feedback": "Great coverage"
    },
    {
        "customer_id": 102,
        "feedback": "Fast internet"
    },
    {
        "customer_id": 103,
        "feedback": "Friendly customer service"
    }
]

In this script, feedback_data already contains two entries. Each entry is a dictionary with customer_id and feedback.

 

Appending Multiple Elements using extend()

Python extend()method allows you to append multiple elements to a list in a single operation.

Now, suppose you receive a batch of new tower data that needs to be added to the existing array.

Instead of appending each item individually, you can use extend() to add them all in one go.

import json
tower_data = [
    {"tower_id": 1001, "location": "Downtown"},
    {"tower_id": 1002, "location": "Suburbs"}
]

# Data to append
new_towers = [
    {"tower_id": 1003, "location": "Industrial Area"},
    {"tower_id": 1004, "location": "Rural"}
]
tower_data.extend(new_towers)
print(json.dumps(tower_data, indent=4))

Output:

[
    {
        "tower_id": 1001,
        "location": "Downtown"
    },
    {
        "tower_id": 1002,
        "location": "Suburbs"
    },
    {
        "tower_id": 1003,
        "location": "Industrial Area"
    },
    {
        "tower_id": 1004,
        "location": "Rural"
    }
]

In this script, tower_data is an array of dictionaries, each representing a telecom tower’s data. new_towers is a list of new tower records.

This makes extend() more efficient than append() for adding multiple items, as it avoids the overhead of multiple method calls.

 

Appending to Nested Element

Here’s how to append to an existing plan’s tier list:

import json
telecom_plans = [
    {
        "plan_id": "PlanA",
        "tiers": [
            {"tier_name": "Basic", "features": ["2GB Data", "100 Minutes"]},
            {"tier_name": "Pro", "features": ["5GB Data", "500 Minutes"]}
        ]
    },
    {
        "plan_id": "PlanB",
        "tiers": [
            {"tier_name": "Standard", "features": ["10GB Data", "Unlimited Texts"]}
        ]
    }
]

# New tier to append to PlanA
new_tier = {"tier_name": "Advanced", "features": ["10GB Data", "Unlimited Calls"]}

# Locate PlanA and append the new tier to its tiers
for plan in telecom_plans:
    if plan["plan_id"] == "PlanA":
        plan["tiers"].append(new_tier)
        break
print(json.dumps(telecom_plans, indent=4))

Output:

[
    {
        "plan_id": "PlanA",
        "tiers": [
            {
                "tier_name": "Basic",
                "features": ["2GB Data", "100 Minutes"]
            },
            {
                "tier_name": "Pro",
                "features": ["5GB Data", "500 Minutes"]
            },
            {
                "tier_name": "Advanced",
                "features": ["10GB Data", "Unlimited Calls"]
            }
        ]
    },
    {
        "plan_id": "PlanB",
        "tiers": [
            {
                "tier_name": "Standard",
                "features": ["10GB Data", "Unlimited Texts"]
            }
        ]
    }
]

In this script, we first identify the plan to which we want to add the new tier (in this case, “PlanA”).

We use a for loop to iterate through the telecom_plans array. When we find “PlanA”, we append the new_tier to its tiers list using the append() method, which adds the new tier to the end of the existing tier list.

 

Appending to a JSON Array Loaded from a File

Let’s go through how to append new data to a JSON array that is loaded from a file:

1. Read the JSON file: Load the existing JSON data into Python.
2. Append the data: Append new elements to the loaded JSON array.
3. Write back to the file: Save the updated array back to the JSON file.

First, assume we have a JSON file named telecom_data.json with the following content:

[
    {
        "user_id": 1001,
        "usage": "5GB"
    },
    {
        "user_id": 1002,
        "usage": "10GB"
    }
]

Now, let’s append a new user’s data to this file:

import json
file_path = 'telecom_data.json'
with open(file_path, 'r') as file:
    data = json.load(file)
new_user_data = {"user_id": 1003, "usage": "8GB"}
data.append(new_user_data)
with open(file_path, 'w') as file:
    json.dump(data, file, indent=4)
print("New user data appended successfully.")

This script reads the existing JSON array from telecom_data.json, appends the new_user_data to this array, and then writes the updated array back to the same file.

The use of with open() ensures that the file is properly closed after its contents are read and written.