Day 45/100 – Reading/Writing JSON in Python

Welcome to Day 45 of the 100 Days of Python series!
Today, we’ll explore how to work with JSON (JavaScript Object Notation) in Python — a common data format used in APIs, configuration files, and data exchange between systems.

1. What is JSON?

• JSON is a lightweight data-interchange format.
• It is human-readable and language-independent.
• It uses a key-value pair structure similar to Python dictionaries.

Example JSON:

{ "name": "Alice", "age": 25, "skills": ["Python", "Data Science"] } 

2. Python’s json Module

Python provides a built-in json module to:

• Parse JSON into Python objects.
• Convert Python objects into JSON strings.

import json 

3. Reading JSON (Deserialization)

To read JSON from a file and convert it into a Python object:

import json with open("data.json", "r") as file: data = json.load(file) print(data) print(type(data)) # dict 

Key Method:

• json.load(file) → Reads JSON from a file and converts it to a Python object.

4. Writing JSON (Serialization)

To write Python objects to a JSON file:

data = { "name": "Alice", "age": 25, "skills": ["Python", "Data Science"] } with open("data.json", "w") as file: json.dump(data, file, indent=4) 

Key Method:

• json.dump(obj, file, indent=4) → Writes Python objects to a file in JSON format.
• indent makes it human-readable.

5. Converting JSON Strings

Sometimes you work with JSON from APIs, which comes as a string.

String to Python Object:

json_string = '{"name": "Bob", "age": 30}' data = json.loads(json_string) print(data["name"]) # Bob 

Python Object to JSON String:

data = {"name": "Charlie", "age": 22} json_str = json.dumps(data, indent=2) print(json_str) 

6. Common Pitfalls

• JSON keys must be strings.
• JSON cannot store Python-specific objects like sets or functions directly.
• Use default=str when serializing objects like datetime.

7. Mini Example

import json user = { "username": "tech_guru", "active": True, "followers": 1050 } # Save to file with open("user.json", "w") as f: json.dump(user, f, indent=4) # Read from file with open("user.json", "r") as f: loaded_user = json.load(f) print(loaded_user) 

Notes

• Serialization = Python → JSON (dump, dumps)
• Deserialization = JSON → Python (load, loads)
• Always handle file operations with with to ensure proper closure.

Challenge

Create a Python program that:

1. Reads user details (name, age, skills) from input().
2. Saves them to a JSON file.
3. Reads the file and prints the stored details.