4.3. Dataclass Relations

4.3.1. SetUp

>>> from dataclasses import dataclass
>>> from typing import Self

4.3.2. Relation to Objects

>>> @dataclass
... class Group:
...     gid: int
...     name: str
>>>
>>>
>>> @dataclass
... class User:
...     firstname: str
...     lastname: str
...     groups: list[Group]

Usage:

>>> mark = User('Mark', 'Watney', groups=[
...     Group(gid=1, name='users'),
...     Group(gid=2, name='staff'),
...     Group(gid=3, name='admins')])

4.3.3. Relation to Self

• Note, that there are None default friends

• Using an empty list [] as a default value will not work

• Self is available since Python 3.11

• We will cover this topic later

Import:

>>> from typing import Self

Define class:

>>> @dataclass
... class User:
...     firstname: str
...     lastname: str
...     friends: list[Self] = None

Use:

>>> mark = User('Mark', 'Watney', friends=[
...     User('Melissa', 'Lewis'),
...     User('Rick', 'Martinez'),
...     User('Beth', 'Johanssen'),
...     User('Chris', 'Beck'),
...     User('Alex', 'Vogel')])

4.3.4. Assignments