October 13, 2024

Python Tutorials

Python JSON

JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy for humans to read and write, and easy for machines to parse and generate. It is commonly used for transmitting data in web applications, often as a way to encode data in an API. Python provides a built-in module called json to work with JSON data.

1. Importing the JSON Module

The json module is part of Python’s standard library, so you don’t need to install anything extra. You can start using it by simply importing the module:

import json

2. Parsing JSON Strings

To convert a JSON string into a Python dictionary, use the json.loads() function.

2.1. Example: Parsing JSON String

import json

# JSON string
json_string = '{"name": "John", "age": 30, "city": "New York"}'

# Parse JSON string into a Python dictionary
data = json.loads(json_string)

# Accessing data
print(data['name'])  # Output: John
print(data['age'])   # Output: 30

3. Converting Python Objects to JSON

To convert a Python object (such as a dictionary) into a JSON string, use the json.dumps() function.

3.1. Example: Converting Python Dictionary to JSON String

import json

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

# Convert dictionary to JSON string
json_string = json.dumps(data)

# Print JSON string
print(json_string)

4. Reading JSON Data from a File

You can load JSON data from a file using the json.load() function. This function reads a JSON file and converts it into a Python object.

4.1. Example: Reading JSON from a File

import json

# Read JSON data from a file
with open('data.json', 'r') as file:
    data = json.load(file)

# Accessing data
print(data['name'])  # Output: John

5. Writing JSON Data to a File

You can write JSON data to a file using the json.dump() function. This function converts a Python object into a JSON string and writes it to a file.

5.1. Example: Writing JSON to a File

import json

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

# Write JSON data to a file
with open('data.json', 'w') as file:
    json.dump(data, file)

6. Pretty-Printing JSON

When working with JSON, it’s often useful to produce more human-readable output. You can use the indent parameter in json.dumps() or json.dump() to pretty-print JSON data.

6.1. Example: Pretty-Printing JSON Data

import json

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

# Convert dictionary to JSON string with pretty printing
json_string = json.dumps(data, indent=4)

# Print pretty-printed JSON string
print(json_string)

7. Handling JSON Arrays

JSON arrays (lists in Python) can also be parsed and generated using the json module.

7.1. Example: Parsing JSON Array

import json

# JSON string with an array
json_string = '''
[
    {"name": "John", "age": 30},
    {"name": "Jane", "age": 25},
    {"name": "Mike", "age": 40}
]
'''

# Parse JSON string into a Python list
data = json.loads(json_string)

# Accessing data in the array
for person in data:
    print(person['name'])

8. Handling Complex Data Types

The json module can handle basic Python data types like strings, numbers, lists, and dictionaries. For more complex data types like custom objects, you need to provide a way to serialize and deserialize them.

8.1. Example: Custom Object Serialization

import json

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

# Custom serialization function
def person_to_dict(person):
    return {
        "name": person.name,
        "age": person.age
    }

# Create an instance of Person
person = Person("John", 30)

# Serialize the object to JSON
json_string = json.dumps(person, default=person_to_dict)

print(json_string)

9. Error Handling with JSON

When working with JSON data, it’s important to handle errors that may arise during parsing or serialization.

9.1. Example: Handling JSON Decoding Errors

import json

# Incorrect JSON string
json_string = '{"name": "John", "age": 30,'  # Missing closing brace

try:
    data = json.loads(json_string)
except json.JSONDecodeError as e:
    print(f"Error decoding JSON: {e}")

JSON is a widely used format for data interchange, and Python’s built-in json module provides powerful tools to work with JSON data. Whether you need to parse JSON strings, serialize Python objects to JSON, or handle JSON files, the json module makes it easy to work with JSON in your Python applications.

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