Python - dataclass

At its core, a Python dataclass (introduced in Python 3.7) is a decorator used to automatically generate "boilerplate" code for classes that primarily exist to store data.¹

 

 

Instead of manually writing methods like __init__(), __repr__(), and __eq__(), the @dataclass decorator handles them for you based on type hints.²

 

 

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1. The "Before and After"

To understand the usage, look at how much code it saves you:

Without Dataclass:

Python

 

class Order:def __init__(self, order_id: str, amount: float):self.order_id = order_idself.amount = amountdef __repr__(self):return f"Order(order_id={self.order_id!r}, amount={self.amount!r})"def __eq__(self, other):if not isinstance(other, Order): return NotImplementedreturn self.order_id == other.order_id and self.amount == other.amount

With Dataclass:

Python

 

from dataclasses import dataclass@dataclass
class Order:order_id: stramount: float

2. Key Features and Usage

Dataclasses provide several built-in functionalities through parameters in the decorator:³

 

 

• __repr__ (Readable Output): Printing the object shows its contents (e.g., Order(order_id='A1', amount=10.5)) rather than a memory address.

• __eq__ (Comparison): Two different objects with the same data will evaluate as equal (obj1 == obj2 is True).

• Type Hinting: It enforces a clear schema for your data structures, making them easier to read and debug.
  

   

   

• Immutability (frozen=True):⁵ You can make the data "read-only," which also allows the object to be hashed (used as a key in a dictionary).

   

3. Advanced Configuration

You can control specific fields using the field() function to set default values or exclude items from the representation.

Python

 

from dataclasses import dataclass, field@dataclass(frozen=True)
class User:username: str# Logic to create a default list (since [] is mutable and unsafe as a default)roles: list[str] = field(default_factory=list)# Hide sensitive data from the print/repr outputpassword: str = field(repr=False) 

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When should you use it?

• Data Transfer Objects (DTOs): Like the Kafka message payload you shared earlier.

• Configuration settings: Storing app constants or database credentials.

• Internal State: Passing structured data between functions instead of using large tuples or dictionaries (which are harder to track).

Summary Table

Feature	Standard Class	Dataclass
Boilerplate	Manual __init__, __repr__	Automated
Readability	High effort to maintain	High "out of the box"
Comparison	Compares memory address by default	Compares actual data values
Primary Goal	Behavior/Methods	Data Storage