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.