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dataclass

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A dataclass is a class decorator (@dataclass) that automatically generates common methods like __init__, __repr__, and __eq__ based on class fields.

Why use it

• Reduces boilerplate for classes that mostly store data.
• Makes code more readable and easier to maintain.
• Supports defaults, type hints, ordering, immutability, and post-init logic.

Use dataclass when your class is primarily structured data with minimal custom behavior.

Basic example

from dataclasses import dataclass

@dataclass
class User:
    name: str
    age: int = 0

user = User("Pablo", 24)
print(user)  # User(name='Pablo', age=24)

Generated methods explained

• __init__: constructor. Creates the object and assigns field values.
  • Runs when you create an object.
  • Its job is to set up the object’s data (attributes).
  • Example call: User("Pablo", 24) sets name and age.
• __repr__: developer-friendly string representation of the object.
  • Runs when Python needs a developer-friendly text version of the object.
  • Example triggers: print(obj) (if no __str__), typing obj in REPL.
  • Example output: User(name='Pablo', age=24).
• __eq__: equality comparison. Two instances are equal if all fields are equal.
  • Runs when you compare with ==.
  • Example: User("Ana", 20) == User("Ana", 20) returns True.

Useful options

• frozen=True: makes instances immutable.
• order=True: adds comparison methods (<, <=, etc.).
• field(...): customize defaults, metadata, and behavior per field.