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Python JSON

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Python JSON

JSON stands for JavaScript Object Notation.
It is a lightweight data format used for storing and transporting data — commonly used in APIs.

Python provides a built-in module named json to work with JSON data.

import json

✅ JSON in Python vs Python Dictionary

JSON Data Type Python Equivalent
Object {} dict
Array [] list
String str
Number int/float
Boolean True/False
Null None

📌 Converting Python to JSON — json.dumps()

dumps() means Dump as String.

Example:

import json

data = {
“name”: “John”,
“age”: 25,
“city”: “New York”
}

json_string = json.dumps(data)
print(json_string)

▶️ Output:

{"name": "John", "age": 25, "city": "New York"}

🎨 Formatting JSON Output

print(json.dumps(data, indent=4))

Additional formatting options:

Argument Meaning
indent Pretty formatting
sort_keys=True Sorts keys alphabetically
separators=(",", ": ") Controls spacing

Example:

print(json.dumps(data, indent=4, sort_keys=True))

🔄 Converting JSON to Python — json.loads()

loads() means Load from String.

json_data = '{"name": "John", "age": 25, "city": "New York"}'

python_dict = json.loads(json_data)
print(python_dict)
print(type(python_dict))

📁 Working with JSON Files

📝 Write JSON to File — json.dump()

data = {"name": "Alice", "age": 30, "city": "London"}

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

📥 Read JSON from File — json.load()

with open("data.json", "r") as file:
result = json.load(file)print(result)

🚀 JSON with Lists

people_json = '''
[
{"name": "John", "age": 25},
{"name": "Emma", "age": 28}
]
'''people = json.loads(people_json)
print(people[1][“name”])

🧪 Converting Python Objects

Python can serialize only basic types.
To convert custom objects, we use:

Option 1 — Convert manually

class Student:
def __init__(self, name, roll):
self.name = name
self.roll = rollstudent = Student(“Raj”, 101)json_data = json.dumps(student.__dict__)
print(json_data)

Option 2 — Using default Parameter

def encode_student(o):
return o.__dict__json_data = json.dumps(student, default=encode_student)
print(json_data)

⚠️ Errors to Avoid

❌ JSON strings must use double quotes ", not '.

wrong = "{'name': 'John'}" # invalid JSON
correct = '{"name": "John"}'

🎯 Summary Table

Action Function
Python ➡ JSON (string) json.dumps()
JSON ➡ Python (string) json.loads()
Write JSON to file json.dump()
Read JSON from file json.load()

🧹 Mini Practical Example

import json

student = {
“name”: “Amit”,
“marks”: [85, 90, 92],
“passed”: True
}

# Save to file
with open(“student.json”, “w”) as f:
json.dump(student, f, indent=4)

# Read from file
with open(“student.json”, “r”) as f:
data = json.load(f)

print(data)

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Sanjit Sinha — Web Developer | PHP • Laravel • CodeIgniter • MySQL • Bootstrap Founder, CodeCapsule — Student projects & practical coding guides. Email: info@codecapsule.in • Website: CodeCapsule.in

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