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Operations with JSON Files

Operations with JSON Files in Python

JSON files have become increasingly popular in recent years due to their compatibility with web-based systems. JSON, or JavaScript Object Notation, is a lightweight format for data exchange, making it a popular choice for web applications. Python has powerful tools for working with JSON files. In this article, we will explore how to read and manipulate JSON files, and how to use JSON files in practical applications.

How to Use JSON with Python

To read, parse, and write JSON files, you can use json Python library. Here are some examples:

Reading from a JSON file

To read a JSON file, you can use the load() function from the json module. Here's an example that reads a JSON file called data.json:

import json

with open('data.json') as f:
    data = json.load(f)


JSON Parsing

If you have a JSON string and want to parse json in Python, you can use the loads() function from the json module. Here's an example:

import json

json_string = '{"name": "John", "age": 30, "city": "New York"}'
data = json.loads(json_string)


Writing a JSON object to a file

To write JSON data to a file, you can use the json.dump() function from the json module. Here's an example:

import json

data = {"name": "John", "age": 30, "city": "New York"}

with open('data.json', 'w') as f:
    json.dump(data, f)

In this example, we have shown how to save dictionary as JSON in Python.

How to Load a JSON File

JSON format is a widely used standard for data exchange. Python provides a built-in module called json to work with JSON data.

The json.loads() method is used to load JSON data from a string. We can use this method to load JSON data from a file by first reading the file contents into a string and then using json.loads() like this:

import json

# Read the file contents into a string
with open('file.json') as f:
    json_str =

# Load the data from the string
data = json.loads(json_str)

# Access the data

In the above code, we first read the contents of the JSON file file.json into the json_str variable using We then loading JSON file with data from the string using json.loads(json_str). The JSON data is now stored in the data variable, which we can access as needed.

How to Write a JSON Pretty Object to a File

To print JSON in a more readable and organized format, you need to use the pretty_print flag. This flag will format the JSON by adding indentation, line breaks, and spaces between the elements. Below are two ways to write JSON pretty to a file.

import json

data = {'name': 'John', 'age': 30, 'city': 'New York'}

with open('data.json', 'w') as file:
    json.dump(data, file, indent=4, sort_keys=True)

In this example, we have used the json.dump() method to convert the dictionary object data to JSON and saved it to a file data.json. We have set the indent parameter to 4 to add indentation, and sort_keys parameter to True to sort the keys alphabetically.

Common Errors with JSON Files

When working with JSON files in Python, you may encounter common errors that can affect the loading, parsing, and processing of JSON data. One such error is the ValueError: Extra data error. This error occurs when there is additional data present in the JSON file that is not compatible with the expected JSON structure.

Example 1: A Loading of JSON with Extra Data

import json

data = '{"name": "John", "age": 25} {"name": "Alice", "age": 30}'

    json_data = json.loads(data)
except ValueError as e:
    print("Error:", str(e))

In this example, the data variable contains two JSON objects separated by a space. When we try to load this data using json.loads(), it raises a ValueError with the message Extra data because multiple JSON objects are not valid in a single JSON file.

Example 2: Read a JSON File with Extra Data

import json

    with open("data.json", "r") as file:
        json_data = json.load(file)
except ValueError as e:
    print("Error:", str(e))

In this example, we are reading JSON data from a file called data.json. If the file contains extra data that does not conform to the expected JSON structure, the json.load() method will raise a ValueError.

To handle the ValueError: Extra data error, you can catch the exception using a try-except block, as shown in the examples. This allows you to gracefully handle the error and provide appropriate feedback or take alternative actions.

When encountering this error, it's important to carefully examine the JSON file to ensure its validity. Verify that the JSON structure is correct and there are no additional or unexpected data present.

Updated: 07/01/2023 - 19:59
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Python engineer, expert in third-party web services integration.