139 – Reduce boilerplate with dataclasses

The module dataclasses provides a decorator dataclass that you’re supposed to use on classes. The decorator dataclass reduces the need to write boilerplate code by adding the dunder methods __init__, __eq__, and __repr__, to the class that is decorated.

To create a dataclass, all you need is to define the attributes that are relevant by listing them in the class body along with an annotation of their type:

from dataclasses import dataclass

@dataclass
class Person:
    first: str
    last : str

The four lines of code that define the class Person as a dataclass are roughly equivalent to the following handwritten definition:

class Person:
    def __init__(self, first, last):
        self.first = first
        self.last = last

    def __eq__(self, other):
        if isinstance(other, Person):
            return self.first == other.first and self.last == other.last
        return NotImplemented

    def __repr__(self):
        cls = type(self).__name__
        return f"{cls}(first={self.first!r}, last={self.last!r})"