How to Parse JSON in Python: Read, Write & Work With JSON Files

Working with JSON in Python: A Complete Guide

Quick answer: Python’s json module provides simple methods to parse JSON strings (json.loads()), read JSON files (json.load()), and write JSON data (json.dumps() and json.dump()).

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What Is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based format for storing and transmitting data. It’s the universal standard for data exchange across APIs, configuration files, and databases.

JSON structure:

• Data organized in key-value pairs
• Keys must be strings
• Values can be strings, numbers, booleans, arrays, objects, or null

Example JSON array:

json

[
  {
    "name": "John",
    "age": 17
  },
  {
    "name": "Alice",
    "age": 24
  }
]

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Reading JSON in Python

From a JSON String

When you get JSON from an API, it’s usually a string:

python

import json
import requests

response = requests.get("https://jsonplaceholder.typicode.com/todos/1")
todo_string = response.text

# Convert string to Python dictionary
todo_dict = json.loads(todo_string)

print(todo_dict["id"])      # 1
print(todo_dict["title"])    # delectus aut autem

From a JSON File

When data comes from a .json file:

python

import json

with open("todos.json", "r") as file:
    todos = json.load(file)  # Returns Python list/dict

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Modifying JSON Data

Once parsed, JSON becomes regular Python data structures you can manipulate:

python

def capitalize_title(todo):
    todo["title"] = todo["title"].capitalize()
    return todo

# Modify the dictionary
todo_dict_capitalized = capitalize_title(todo_dict)

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Writing JSON in Python

To a JSON String

Convert Python objects back to JSON strings:

python

# Convert dictionary to JSON string
todo_json = json.dumps(todo_dict_capitalized)
print(todo_json)  # {"userId": 1, "id": 1, "title": "Delectus aut autem", "completed": false}

# Pretty-print with indentation
todo_json_pretty = json.dumps(todo_dict_capitalized, indent=4)
print(todo_json_pretty)

To a JSON File

Write Python data directly to a file:

python

with open("capitalized_todos.json", "w") as file:
    json.dump(todos, file, indent=4)

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Working with Nested JSON

Access deeply nested data safely:

python

data = {
    "user": {
        "profile": {
            "name": "Alice",
            "age": 30
        }
    }
}

# Using square brackets
name = data["user"]["profile"]["name"]

# Using .get() (safer for missing keys)
age = data.get("user", {}).get("profile", {}).get("age")

For deeply nested or unpredictable structures, use a recursive function:

python

def find_key(data, target):
    if isinstance(data, dict):
        if target in data:
            return data[target]
        for value in data.values():
            result = find_key(value, target)
            if result:
                return result
    elif isinstance(data, list):
        for item in data:
            result = find_key(item, target)
            if result:
                return result
    return None

# Usage
email = find_key(complex_data, "email")

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Custom Objects with JSON

Decoding JSON to Custom Objects

Use object_hook to convert JSON to your own classes:

python

class Todo:
    def __init__(self, user_id, id, title, completed):
        self.user_id = user_id
        self.id = id
        self.title = title
        self.completed = completed
    
    def capitalize_title(self):
        self.title = self.title.capitalize()
        return self
    
    @classmethod
    def from_dict(cls, data):
        return cls(
            user_id=data["userId"],
            id=data["id"],
            title=data["title"],
            completed=data["completed"]
        )

# Load JSON directly into Todo objects
with open("todos.json", "r") as file:
    todos = json.load(file, object_hook=Todo.from_dict)

# Now you can use class methods
for todo in todos:
    todo.capitalize_title()

Encoding Custom Objects to JSON

Create a custom encoder:

python

class TodoEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Todo):
            return {
                "userId": obj.user_id,
                "id": obj.id,
                "title": obj.title,
                "completed": obj.completed
            }
        return super().default(obj)

# Write custom objects to JSON file
with open("todos_export.json", "w") as file:
    json.dump(todos, file, cls=TodoEncoder, indent=4)

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Pretty-Printing JSON

Make JSON human-readable:

python

import json

ugly_json = '{"userId":1,"id":1,"title":"delectus aut autem","completed":false}'
parsed = json.loads(ugly_json)

# Basic pretty print
print(json.dumps(parsed, indent=4))

# Custom formatting
print(json.dumps(
    parsed, 
    indent=4, 
    separators=(", ", ": "), 
    sort_keys=True
))

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Key Functions Comparison

Function	Purpose	Input	Output
json.load()	Read JSON file	File object	Python object
json.loads()	Parse JSON string	String	Python object
json.dump()	Write to JSON file	Python object + file	None (writes file)
json.dumps()	Convert to JSON string	Python object	JSON string

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Common JSON to Python Type Mapping

JSON Type	Python Type
Object	dict
Array	list
String	str
Number	int or float
Boolean	bool
Null	None

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Error Handling

Always handle JSON parsing errors:

python

import json

try:
    with open("data.json", "r") as file:
        data = json.load(file)
except FileNotFoundError:
    print("File not found")
except json.JSONDecodeError as e:
    print(f"Invalid JSON: {e}")

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Summary

Task	Method
Parse JSON string → Python dict	json.loads()
Read JSON file → Python object	json.load()
Convert Python dict → JSON string	json.dumps()
Write Python object → JSON file	json.dump()
Custom object decoding	object_hook parameter
Custom object encoding	Subclass JSONEncoder
Pretty print	indent parameter
Handle missing keys	.get() or recursive search

Python’s json module makes working with JSON data straightforward—whether you’re consuming APIs, reading configuration files, or exporting data for other applications.