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OOP · medium

25. Dataclasses

Boilerplate-free classes for structured data.

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`@dataclass` auto-generates `__init__`, `__repr__`, and `__eq__` from type-annotated fields, cutting boilerplate for simple data-holding classes.

python
from dataclasses import dataclass, field

@dataclass
class Transaction:
    sender: str
    receiver: str
    amount: float
    tags: list = field(default_factory=list)

tx = Transaction("0xa", "0xb", 1.5)
tx2 = Transaction("0xa", "0xb", 1.5)
tx == tx2   # True, dataclasses compare by field values

`field(default_factory=list)` avoids the mutable-default-argument pitfall for list/dict fields. Pass `frozen=True` to `@dataclass` to make instances immutable (raises on attribute assignment).

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  1. 1. What does @dataclass automatically generate?

  2. 2. Why use `field(default_factory=list)` instead of `= []`?

  3. 3. What does `frozen=True` do on a dataclass?

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