@dataclass
- Python course
- Intermediate
- Lesson 21/116
- 5 min
Learn data classes with @dataclass.
The @dataclass decorator
The @dataclass decorator simplifies class boilerplate. From type-annotated attributes it auto-generates __init__, __repr__ and __eq__ methods.
Example: from dataclasses import dataclass\n@dataclass\nclass Product:\n name: str\n price: float. This removes the need for hand-written __init__ and __repr__. The instance Product("Pen", 5.0) is ready; print(p) shows a clean representation. It is useful for data-carrying classes with encapsulation.
Type annotations
In a @dataclass class, each attribute is written with a type annotation: name: str, price: float. These annotations tell the decorator which attributes to generate.
For mutable defaults, field(default_factory=list) is used; [] cannot be written directly. In this lesson we'll only use constant defaults. The annotation does not break encapsulation; it just states the data layout.
Practice Define the Product data class
First write from dataclasses import dataclass. Then add the @dataclass decorator and class Product:. In the body add the annotations name: str and price: float. Then create an instance with p = Product("Pen", 5.0) and print it with print(p).
Starter code
# Define the Product data classSample solution
# Define the Product data class
from dataclasses import dataclass
@dataclass
class Product:
name: str
price: float
p = Product("Pen", 5.0)
print(p)Expected output
Product(name='Pen', price=5.0)
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which decorator auto-generates __init__?
- @dataclass Correct answer
- @classmethod
- @property
- @staticmethod
Explanation: @dataclass generates __init__ from type-annotated attributes.
2 Complete the dataclass import
from dataclasses import ____
@dataclass
class Product:
name: str
price: floatfrom dataclasses import dataclass
@dataclass
class Product:
name: str
price: floatExplanation: The dataclass function is imported from the dataclasses module.
3 Match the @dataclass concepts
| Term | Meaning |
|---|---|
@dataclass |
Decorator |
name: str |
Type annotation |
__repr__ |
Auto-generated |