19.3. Dataclass Relations
19.3.1. SetUp
>>> from dataclasses import dataclass
>>> from typing import Self
19.3.2. Composition
>>> @dataclass
... class Group:
... gid: int
... name: str
>>>
>>>
>>> @dataclass
... class User:
... firstname: str
... lastname: str
... group: Group
Usage:
>>> mark = User('Alice', 'Apricot', group=Group(gid=1, name='users'))
19.3.3. Aggregation
>>> @dataclass
... class Group:
... gid: int
... name: str
>>>
>>>
>>> @dataclass
... class User:
... firstname: str
... lastname: str
... groups: list[Group]
Usage:
>>> mark = User('Alice', 'Apricot', groups=[
... Group(gid=1, name='users'),
... Group(gid=2, name='staff'),
... Group(gid=3, name='admins'),
... ])
19.3.4. Forward Reference
>>> @dataclass
... class User:
... firstname: str
... lastname: str
... friends: list[Self] | None = None
Usage:
>>> alice = User('Alice', 'Apricot', friends=[
... User('Bob', 'Blackthorn'),
... User('Carol', 'Corn'),
... User('Dave', 'Durian'),
... User('Eve', 'Elderberry'),
... User('Mallory', 'Melon'),
... ])
19.3.5. Assignments
# %% About
# - Name: Dataclass Relations Composition
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1
# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author
# %% English
# 1. Modify the `User` dataclass to have an additional attribute `group`
# 2. Use composition
# 3. Run doctests - all must succeed
# %% Polish
# 1. Zmodyfikuj dataclass `User`, aby miał dodatkowy atrybut `group`
# 2. Użyj kompozycji
# 3. Uruchom doctesty - wszystkie muszą się powieść
# %% Expected
# @dataclass
# class User:
# firstname: str
# lastname: str
# group: ...
# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'
>>> from inspect import isclass
>>> assert isclass(User), \
'Object `User` has an invalid type; expected: `class`.'
>>> result = User('Alice', 'Apricot', group=Group(gid=1, name='users'))
>>>
>>> assert type(result) is User, \
'Result has an invalid type; expected: `User`.'
>>> assert hasattr(result, 'group'), \
'Result has an invalid attribute; expected: to have an attribute `group`.'
>>> assert type(result.group) is Group, \
'Result has an invalid attribute; expected: `group` to be of type `Group`.'
"""
# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`
# %% Imports
from dataclasses import dataclass
# %% Types
User: type
Group: type
# %% Data
@dataclass
class Group:
gid: int
name: str
# %% Result
@dataclass
class User:
firstname: str
lastname: str
# %% About
# - Name: Dataclass Relations Aggregation
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1
# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author
# %% English
# 1. Modify the `User` dataclass to have an additional attribute `groups`
# 2. Use aggregation
# 3. Run doctests - all must succeed
# %% Polish
# 1. Zmodyfikuj dataclass `User`, aby miał dodatkowy atrybut `groups`
# 2. Użyj agregacji
# 3. Uruchom doctesty - wszystkie muszą się powieść
# %% Expected
# @dataclass
# class User:
# firstname: str
# lastname: str
# groups: ...
# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'
>>> from inspect import isclass
>>> assert isclass(User), \
'Object `User` has an invalid type; expected: `class`.'
>>> result = User('Alice', 'Apricot', groups=[
... Group(gid=1, name='users'),
... Group(gid=2, name='staff'),
... ])
>>>
>>> assert type(result) is User, \
'Result has an invalid type; expected: `User`.'
>>> assert hasattr(result, 'groups'), \
'Result has an invalid attribute; expected: to have an attribute `groups`.'
>>> assert type(result.groups) is list, \
'Result has an invalid attribute; expected: `groups` to be of type `list`.'
"""
# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`
# %% Imports
from dataclasses import dataclass
# %% Types
User: type
Group: type
# %% Data
@dataclass
class Group:
gid: int
name: str
# %% Result
@dataclass
class User:
firstname: str
lastname: str
# %% About
# - Name: Dataclass Relations Composition
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1
# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author
# %% English
# 1. Modify the `User` dataclass to have an optional attribute `friend`
# 2. Use forward reference
# 3. Run doctests - all must succeed
# %% Polish
# 1. Zmodyfikuj dataclass `User`, aby miał opcjonalny atrybut `friend`
# 2. Użyj odwołania w przód
# 3. Uruchom doctesty - wszystkie muszą się powieść
# %% Expected
# @dataclass
# class User:
# firstname: str
# lastname: str
# friend: ...
# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 14), \
'Python has an is invalid version; expected: `3.14` or newer.'
>>> from inspect import isclass
>>> assert isclass(User), \
'Object `User` has an invalid type; expected: `class`.'
>>> result = User('Alice', 'Apricot', friend=User('Bob', 'Blackthorn'))
>>>
>>> assert type(result) is User, \
'Result has an invalid type; expected: `User`.'
>>> assert hasattr(result, 'friend'), \
'Result has an invalid attribute; expected: to have an attribute `friend`.'
>>> assert type(result.friend) is User, \
'Result has an invalid attribute; expected: `friend` to be of type `User`.'
"""
# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`
# %% Imports
from dataclasses import dataclass
# %% Types
User: type
# %% Data
@dataclass
class Group:
gid: int
name: str
# %% Result
@dataclass
class User:
firstname: str
lastname: str
# %% About
# - Name: Dataclass Relations Syntax
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1
# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author
# %% English
# 1. Use Dataclass to define class `Point` with attributes:
# - `x: int` with default value `0`
# - `y: int` with default value `0`
# 2. Use Dataclass to define class `Path` with attributes:
# - `points: list[Point]`
# 3. Run doctests - all must succeed
# %% Polish
# 1. Użyj Dataclass do zdefiniowania klasy `Point` z atrybutami:
# - `x: int` z domyślną wartością `0`
# - `y: int` z domyślną wartością `0`
# 2. Użyj Dataclass do zdefiniowania klasy `Path` z atrybutami:
# - `points: list[Point]`
# 3. Uruchom doctesty - wszystkie muszą się powieść
# %% Expected
# @dataclass
# class Path:
# points: ...
# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'
>>> from inspect import isclass
>>> assert isclass(Point), \
'Object `Point` has an invalid type; expected: `class`.'
>>> assert isclass(Path), \
'Object `Path` has an invalid type; expected: `class`.'
>>> assert hasattr(Point, 'x'), \
'Object `Point` has an invalid attribute; expected: to have an attribute `x`.'
>>> assert hasattr(Point, 'y'), \
'Object `Point` has an invalid attribute; expected: to have an attribute `y`.'
>>> Point()
Point(x=0, y=0)
>>> Point(x=0, y=0)
Point(x=0, y=0)
>>> Point(x=1, y=2)
Point(x=1, y=2)
>>> Path([Point(x=0, y=0),
... Point(x=0, y=1),
... Point(x=1, y=0)])
Path(points=[Point(x=0, y=0), Point(x=0, y=1), Point(x=1, y=0)])
"""
# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`
# %% Imports
from dataclasses import dataclass
# %% Types
Point: type
Path: type
# %% Data
@dataclass
class Point:
x: int = 0
y: int = 0
# %% Result
@dataclass
class Path:
...