# Created on savesnippets.com · https://savesnippets.com/5KNOhrniloyq8M
from dataclasses import dataclass, field

@dataclass(frozen=True, slots=True)
class User:
    id:    int
    name:  str
    email: str
    roles: list[str] = field(default_factory=list)   # never use [] as default!

u = User(id=42, name="Alice", email="a@x.com", roles=["admin"])
print(u)
# User(id=42, name='Alice', email='a@x.com', roles=['admin'])

# Frozen → can't mutate; equality + hash come for free.
# u.name = "Bob"            # FrozenInstanceError
print(hash(u))              # works because frozen=True