191 – Frozen dataclasses

Frozen dataclasses are created by setting frozen=True in the decorator dataclass:

from dataclasses import dataclass

@dataclass(frozen=True)
class Point:
    x: int
    y: int

By being set to frozen, data classes become immutable and hashable, making them usable as dictionary keys or as set elements:

p = Point(0, 0)

my_dict = {p: "origin"}
print(my_dict)
# {Point(x=0, y=0): 'origin'}

Surprisingly, frozen dataclasses pay a tiny performance penalty.