JSON Structure & Data Types

In this lesson, you will learn the fundamental data types allowed in JSON and how Python maps its native types to JSON.

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1. Supported JSON Data Types

JSON supports 6 core data types:

JSON Data Type	Python Equivalent	Example
Object	dict (Dictionary)	{"name": "Sai", "age": 25}
Array	list (List)	["Python", "Machine Learning"]
String	str (Text)	"Hyderabad"
Number	int or float	100 or 98.6
Boolean	bool	true or false
Null	None	null

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2. Nested JSON: Real-World Example

In real-world applications (like e-commerce apps or AI APIs), JSON objects are rarely flat. They contain nested objects and arrays inside objects:

{
  "order_id": "ORD-98421",
  "customer": {
    "name": "Ananya Sharma",
    "city": "Vijayawada",
    "is_prime_member": true
  },
  "items": [
    {"product": "Wireless Mouse", "price": 499, "qty": 1},
    {"product": "USB-C Cable", "price": 199, "qty": 2}
  ],
  "discount_code": null,
  "total_amount": 897.00
}

Notice:

1. customer is a nested JSON object (maps to a nested Python dictionary).
2. items is a JSON array of objects (maps to a Python list of dictionaries).
3. discount_code is null (maps to Python None).

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3. How to Navigate Nested JSON in Python

Once this JSON is converted into a Python dictionary, you navigate it using standard dictionary and list bracket notation:

order = {
    "order_id": "ORD-98421",
    "customer": {"name": "Ananya Sharma", "city": "Vijayawada"},
    "items": [
        {"product": "Wireless Mouse", "price": 499},
        {"product": "USB-C Cable", "price": 199}
    ]
}

# 1. Access customer name:
print(order["customer"]["name"])  # Output: Ananya Sharma

# 2. Access the first item's product name:
print(order["items"][0]["product"])  # Output: Wireless Mouse

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Quick Summary

• JSON Objects ({}): Unordered sets of key-value pairs matching Python dictionaries.
• JSON Arrays ([]): Ordered lists of values matching Python lists.
• Primitive Types: Strings (double-quoted), numbers (integer/float), booleans (true/false), and null.
• Deep Nesting: Objects and Arrays can nest arbitrarily to represent complex hierarchical data models (like e-commerce orders or REST responses).

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What's Next?

Now let's learn how to read and write JSON strings and disk files using Python's json module in Reading & Writing JSON!