Working with JSON in Python: A Practical Guide

JSON in Python is something you’ll work with constantly — APIs return JSON, config files use JSON, databases store JSON. The good news is Python’s built-in json module makes it simple. No installation needed.

Reading JSON: Parsing Strings and Files

JSON looks like a Python dictionary, but it’s a string. The json module converts between the two.

import json

# Parse a JSON string
json_string = '{"name": "Kaikobud", "age": 28, "skills": ["Python", "Go"]}'
data = json.loads(json_string)  # loads = "load string"

print(data["name"])    # Kaikobud
print(data["skills"])  # ['Python', 'Go']

To read JSON from a file:

with open("config.json", "r") as f:
    config = json.load(f)  # load (no 's') reads from a file object

print(config["database_host"])

The pattern is simple: json.loads() for strings, json.load() for files.

Writing JSON: Converting Python to JSON

import json

user = {
    "id": 1,
    "name": "Kaikobud",
    "active": True,
    "score": 9.5
}

# Convert to JSON string
json_string = json.dumps(user, indent=2)
print(json_string)

# Write to a file
with open("output.json", "w") as f:
    json.dump(user, f, indent=2)

The indent=2 parameter makes the output human-readable. Without it, everything is on one line.

Handling Dates and Custom Types

Python’s json module doesn’t know how to serialize datetime objects by default. Use a custom encoder:

from datetime import datetime
import json

class DateEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        return super().default(obj)

data = {"created_at": datetime.now()}
print(json.dumps(data, cls=DateEncoder))

Conclusion

The json module is essential for working with JSON in Python. Remember: loads/dumps for strings, load/dump for files. You’ll use this every time you consume an API, read a config, or build a backend service. Master these four functions and you’re set.

Read next: Building a REST API with Python and Flask

External resource: Python Docs — json module