@dataclass basics

Learn data classes with @dataclass.

@dataclass basics

The @dataclass decorator turns a class into a dataclass. From the fields you write in the body, it auto-generates the constructor, __repr__ and __eq__ methods. It is imported from the dataclasses module.

Example: @dataclass\nclass Point:\n x: int = 0\n y: int = 0. This short definition gives you the Point(x=0, y=0) call, print(p) and p1 == p2 comparison automatically. Each field name must have a type annotation; without it, the dataclass does not work.

Type annotations required

In a dataclass, each field name must come with a type. The line x: int = 0 has int as the type and 0 as the default. Without a type annotation, @dataclass does not see the field.

The type is only a hint; it is not enforced at runtime. So you can write int and later assign p.x = "text"; Python allows it. Still, writing the type correctly improves readability and tooling support.

Exercise Define the Point dataclass

Start with from dataclasses import dataclass. Define a Point class with @dataclass; include fields x: int = 0 and y: int = 0. Then create an instance with p = Point(3, 4) and print with print(p.x, p.y).

Show example solution

# Define the Point dataclass
from dataclasses import dataclass

@dataclass
class Point:
    x: int = 0
    y: int = 0

p = Point(3, 4)
print(p.x, p.y)

Test yourself

What does @dataclass generate automatically?
- Only __str__
- Only __init__
- __init__, __repr__, __eq__
- Nothing
Show answer

__init__, __repr__, __eq__ — @dataclass auto-generates the constructor, repr and eq methods.

Complete the import line

from dataclasses import ____

@dataclass
class Point:
    x: int = 0
    y: int = 0

Show answer

from dataclasses import dataclass

@dataclass
class Point:
    x: int = 0
    y: int = 0

Match the dataclass parts

@dataclass

Decorator
x: int = 0

Field definition
Point(3, 4)

Instance creation
__eq__

Auto comparison

Next lesson: field()

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