4.6. Inheritance Aggregation

4.6.1. Example

>>> class UserPermissions:
...     pass
>>>
>>> class AdminPermissions:
...     pass
>>>
>>>
>>> class Account:
...     def __init__(self):
...         self.permissions = []

>>> mark = Account()
>>> mark.permissions.append(UserPermissions())
>>> mark.permissions.append(AdminPermissions())

4.6.2. Diagram

4.6.3. Code

class TupleSerializer:
    def astuple(self, instance):
        data = [v for v in vars(instance).values()]
        return tuple(data)


class DictSerializer:
    def asdict(self, instance):
        data = {k: v for k, v in vars(instance).items()
                if not k.startswith('_')}
        return dict(data)


class Account:
    serializers: list = []

    def __init__(self, firstname, lastname):
        self.firstname = firstname
        self.lastname = lastname

    def astuple(self):
        for serializer in self.serializers:
            if hasattr(serializer, 'astuple'):
                return serializer.astuple(self)
        clsname = self.__class__.__name__
        error = f"'{clsname}' object has no attribute 'astuple'"
        raise AttributeError(error)

    def asdict(self):
        for serializer in self.serializers:
            if hasattr(serializer, 'asdict'):
                return serializer.asdict(self)
        clsname = self.__class__.__name__
        error = f"'{clsname}' object has no attribute 'asdict'"
        raise AttributeError(error)


class User(Account):
    serializers = []


class Staff(Account):
    serializers = [TupleSerializer()]


class Admin(Account):
    serializers = [TupleSerializer(), DictSerializer()]

4.6.4. Use Case - 1

>>> class Permission:
...     pass
>>>
>>> class ProfileEdit(Permission):
...     def edit_profile(self): ...
>>>
>>> class ProfileDelete(Permission):
...     def delete_profile(self): ...
>>>
>>> class UserDelete(Permission):
...     def user_delete(self): ...
>>>
>>> class UserEdit(Permission):
...     def user_edit(self): ...
>>>
>>>
>>> class MyAccount:
...     permissions: list[Permission] = []
...
...     def edit_profile(self):
...         for permission in self.permissions:
...             if hasattr(permission, 'edit_profile'):
...                 return permission.edit_profile()
...         raise PermissionError('Cannot edit permission')
>>>
>>> mark = MyAccount()
>>> mark.permissions.append(ProfileEdit())
>>> mark.permissions.append(ProfileDelete())

4.6.5. Assignments

# %% 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

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -v myfile.py`

# %% About
# - Name: Inheritance Aggregation A
# - Difficulty: easy
# - Lines: 2
# - Minutes: 3

# %% English
# 1. Define class `UserPermissions`
# 2. Define class `AdminPermissions`
# 3. Compose `Account` from `UserPermissions`, `AdminPermissions`
# 4. Use aggregation
# 5. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj klasę `UserPermissions`
# 2. Zdefiniuj klasę `AdminPermissions`
# 3. Skomponuj `Account` z klas `UserPermissions`, `AdminPermissions`
# 4. Użyj agregacji
# 5. Uruchom doctesty - wszystkie muszą się powieść

# %% Tests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> from inspect import isclass

>>> assert isclass(UserPermissions)
>>> assert isclass(AdminPermissions)
>>> assert isclass(Account)

>>> result = Account()

>>> assert hasattr(result, 'permissions'), \
'Account instance must have `permissions` attribute'

>>> result.permissions.append(UserPermissions())
>>> result.permissions.append(AdminPermissions())
"""


# Define class `UserPermissions`
# Define class `AdminPermissions`
# Compose `Account` from `UserPermissions`, `AdminPermissions`
# Use composition
# type: type[Account]
...