Dumping Python object to JSON using json.dumps() for JSON Serialization

When working with JSON data in Python, the json.dumps() method is your go-to tool for converting Python objects into JSON strings. It’s part of Python’s built-in json module and offers extensive functionality, including pretty-printing, sorting keys, and handling complex objects. In this guide, we’ll dive into the details of using json.dumps() and its companion, json.dump(), for file-based serialization.

What is JSON?

JSON (JavaScript Object Notation) is a lightweight, human-readable format for structuring data. It’s widely used in web and mobile applications for data exchange and storage. Compared to XML, JSON:

• Uses less space: Smaller file sizes.
• Is easy to read: Human-friendly syntax.
• Is supported universally: Found in Python, JavaScript, Java, C++, Go, PHP, and more.

JSON’s simplicity and efficiency make it an ideal choice for APIs, configuration files, and data serialization.

What is Python Object Serialization?

Serialization refers to encoding Python objects into a format (like JSON) that can be stored in a file, database, or sent over a network. With json.dumps(), you can serialize Python objects into JSON strings, while json.dump() writes them directly to a file.

Why serialize?

• Preserve the object’s state.
• Enable easy data sharing between applications.
• Store structured data in a compact format.

Important: Serialization should be used cautiously for sensitive data, as it’s not inherently secure. Always transmit serialized data over secure connections.

How Does json.dumps() Work?

The json.dumps() method converts Python objects into JSON strings.

Syntax:

json.dumps(obj, *, skipkeys=False, ensure_ascii=True, indent=None, separators=None, sort_keys=False, **kwargs)  

Example:

import json  

data = {"name": "Alice", "age": 30, "city": "New York"}  
json_string = json.dumps(data)  

print(json_string)  # Output: {"name": "Alice", "age": 30, "city": "New York"}  

How to Pretty-Print JSON with json.dumps()?

Pretty-printing improves JSON readability by adding line breaks and indentation. Use the indent parameter:

pretty_json = json.dumps(data, indent=4)  
print(pretty_json)  
# Output:  
# {  
#     "name": "Alice",  
#     "age": 30,  
#     "city": "New York"  
# }  

How to Create Compact JSON?

For compact JSON without unnecessary spaces, use the separators parameter:

compact_json = json.dumps(data, separators=(',', ':'))  
print(compact_json)  # Output: {"name":"Dharmender","age":30,"city":"Bangalore"}  

How to Sort JSON Keys?

Sorting JSON keys can be useful for consistent outputs. Set sort_keys=True:

sorted_json = json.dumps(data, sort_keys=True)  
print(sorted_json)  # Output: {"age": 30, "city": "Bangalore", "name": "Dharmender"}  

Handling Non-ASCII Characters

By default, json.dumps() escapes non-ASCII characters. To include them as-is, use ensure_ascii=False:

data = {"name": "Amit", "country": "India"}  
json_string = json.dumps(data, ensure_ascii=False)  
print(json_string)  # Output: {"name": "Amit", "country": "India"}  

How to Handle Complex Python Objects?

json.dumps() can’t serialize custom or non-basic Python objects like classes. You can fix this by:

1. Custom Encoding:
   Use the default parameter to specify a custom encoder.

class Point:  
    def __init__(self, x, y):  
        self.x = x  
        self.y = y  

def custom_encoder(obj):  
    if isinstance(obj, Point):  
        return {"x": obj.x, "y": obj.y}  
    raise TypeError("Object not serializable")  

point = Point(1, 2)  
json_string = json.dumps(point, default=custom_encoder)  
print(json_string)  # Output: {"x": 1, "y": 2}  

1. Custom JSONEncoder Subclass:
   Extend the JSONEncoder class to handle custom objects.

How to Dump JSON to a File?

Use json.dump() to write JSON directly to a file:

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

How to Skip Invalid Keys?

If your Python object contains non-serializable keys, use skipkeys=True to ignore them:

data = {"name": "Dharmender", "age": 30, "hobby": set([1, 2, 3])}  
json_string = json.dumps(data, skipkeys=True)  
print(json_string)  # Output: {"Dharmender": "Alice", "age": 30}  

Key Differences Between json.dumps() and json.loads()

Feature	json.dumps()	json.loads()
Purpose	Converts Python object to JSON string	Converts JSON string to Python object
Output	JSON string	Python dictionary or list
Common Use Case	Serialization (e.g., saving data to files)	Deserialization (e.g., parsing API responses)

Common Exceptions in json.dumps()

1. TypeError: Thrown for unsupported object types.
   Fix: Use custom encoders or skipkeys=True.
2. Invalid Character Encoding: Non-ASCII characters may cause issues.
   Fix: Use ensure_ascii=False.

Python’s json.dumps() method is a versatile and powerful tool for JSON serialization. Whether you need pretty-printed JSON, compact files, or custom encoding for complex objects, json.dumps() has you covered. With additional parameters like indent, sort_keys, and ensure_ascii, it offers flexibility to meet various needs.

Understanding how to use json.dumps() effectively allows you to manage JSON data seamlessly, making it a must-have skill for Python developers.

Keep Learning 🙂