What is a Data Class and How Does It Work?

🧩 What is a Data Class?

A data class is a class that is mainly used to hold data values. Instead of writing all the methods like __init__ , __repr__, or __eq__ manually, Python provides the dataclasses module (introduced in Python 3.7) to generate them automatically.

👉 In short: Data classes simplify classes that only store data.

🔑 Why Use a Data Class?

Normally, if you want to create a class to hold data, you’d need to write a lot of repetitive code.

Example without Data Class:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return f"Person(name={self.name}, age={self.age})"

p1 = Person("Alice", 25)
print(p1)

Output:

Person(name=Alice, age=25)

This works, but writing the __init__ and __repr__every time is repetitive.

⚡ Using Data Class

With data classes, you can achieve the same with less code.

from dataclasses import dataclass

@dataclass
class Person:
    name: str
    age: int

p1 = Person("Alice", 25)
print(p1)

Output:

Person(name='Alice', age=25)

👉 The dataclass decorator automatically creates __init__ , __repr__, and __eq__ methods for you.

🛠️ Features of Data Classes

1. Automatic __init__ method – No need to manually write constructors.

2. Automatic __repr__ method – Easy-to-read string representation of objects.

3. Automatic __eq__ method – You can compare two objects directly.

Example:

@dataclass
class Person:
    name: str
    age: int

p1 = Person("Alice", 25)
p2 = Person("Alice", 25)
print(p1 == p2)

Output:

True

Here, both objects are equal because their data is the same.

📦 Default Values and Field Options

You can also set default values for attributes.

from dataclasses import dataclass

@dataclass
class Product:
    name: str
    price: float = 0.0  # default value

item = Product("Book")
print(item)

Output:

Product(name='Book', price=0.0)

You can even control behavior using thefield() function:

from dataclasses import dataclass, field

@dataclass
class Product:
    name: str
    tags: list = field(default_factory=list)

item = Product("Book")
print(item.tags)

Output:

[]

🏗️ Immutability with frozen=True

If you want to make your data class immutable (read-only), you can use frozen=True .

@dataclass(frozen=True)
class Point:
    x: int
    y: int

p = Point(2, 3)
print(p.x)

# Trying to modify will raise an error
p.x = 10

Output:

2
Traceback (most recent call last):
  ...
FrozenInstanceError: cannot assign to field 'x'

🔍 Data Class vs Normal Class

Feature	Normal Class	Data Class
Auto __init__	❌ No	✅ Yes
Auto __repr__	❌ No	✅ Yes
Auto __eq__	❌ No	✅ Yes
Less Boilerplate Code	❌ No	✅ Yes

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📌 Summary

Data classes in Python provide a clean and efficient way to store structured data. They automatically handle common methods like __init__, __repr__, and __eq__, which saves time and makes the code easier to read. You can also use advanced features like default values, immutability (frozen=True), and custom field options. If you want to reduce boilerplate code when working with classes that only hold data, data classes are the perfect choice. 🚀