Append to JSON file in Python

In this article, we are going to show you how to append to JSON file in Python. Python has a built-in package called json which lets us working with JSON. There are several ways to do it. But we use a simple way for your easy understanding.

First, you have to know about JSON.

• The expansion of JSON is JavaScript Object Notation.
• Used for data transmission that takes place between a server and a web application.
• It is a collection of key and value pairs.

Python program to append JSON file

Let’s have a look at the following example.

js1.json:

{"Name": "ram", "Age": "20", "Gender": "male"}

import json
dict1= {"City": "chennai"}
with open("js1.json", "r+") as fi:
    data = json.load(fi)
    data.update(dict1)
    fi.seek(0)
    json.dump(data, fi)

In this example, we have imported a json module. The functions used in this program are as follows.

1.loads(): purpose of loads() is to parse the JSON string. It takes JSON string as a parameter and returns the python dictionary object.

• Syntax: json.loads(json_string)

2.update(): this function updates the dictionary with elements from another dictionary object which is a key-value pair. It takes another dictionary as an argument and returns none.

• Syntax: dict.update(other_dict)

3.dumps(): this function converts Python object to JSON string. It takes a Python object as an argument and returns the JSON string.

• Syntax: json.dumps(object)

4.seek(): this function changes the position of a filehandle to a given position. It takes offset(no.of positions to be moved) and from(point of reference) as parameters. When we set the offset value to 0, it points to the beginning of a file.

• Syntax: file.seek(offset,from)

After executing the above program, the JSON file will be modified as follows.

js1.json:

 {"Name": "ram", "Age": "20", "Gender": "male", "City": "chennai"}

I hope that you have learned something useful from this tutorial.

3 responses to “Append to JSON file in Python”

1. Mark Barrett says:

   February 17, 2021 at 6:33 am

   When I try the above I get an error!!!

   Exception has occurred: AttributeError
   ‘list’ object has no attribute ‘update’
   File “/home/delacy/Documents/PyProgs/json/try.py”, line 11, in
   data.update(a_dictionary)
   If I change data,update to data.append it works but adds to the end of the list, if run again it adds another list to the end of the last list????

   I want it to over write!!

   Reply
2. João Frade says:

   March 31, 2021 at 7:12 pm

   What can i do to add for example another gender or another city, so it becames like:
   {“Name”: “ram”, “Age”: “20”, “Gender”: “male”,”female”, “City”: “chennai”,”barcelona”}

   Reply
   • srirma says:

     April 7, 2022 at 9:54 pm

     Jsons have either lists or maps as fields, so “City” needs to have a list as its value, [“chennai”,”barcelona”]

     Reply