16.22. OOP Inheritance Patterns¶

No Inheritance
Single Inheritance
Multilevel Inheritance
Multiple Inheritance (with mixin classes)

single inheritance¶: One class inherits from one other class. Has one parent.
multilevel inheritance¶: One class inherits from other class, and yet another class inherits from it. This creates hierarchical structure.
multiple inheritance¶
mixin classes¶: One class derives from several other classes at once.

16.22.1. Starting Point¶

>>> class Car:
...     pass
...
>>> class Truck:
...     pass
...
...
>>> maluch = Car()
>>> scania = Truck()

16.22.2. No Inheritance¶

>>> class Car:
...     def engine_start(self): ...
...     def engine_stop(self): ...
...
>>> class Truck:
...     def engine_start(self): ...
...     def engine_stop(self): ...
...
...
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()

16.22.3. Single Inheritance¶

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
...
>>> class Car(Vehicle):
...     pass
...
>>> class Truck(Vehicle):
...     pass
...
...
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
...     def window_open(self): ...
...     def window_close(self): ...
...
>>> class Car(Vehicle):
...     pass
...
>>> class Truck(Vehicle):
...     pass
...
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()

Problem:

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
...     def window_open(self): ...
...     def window_close(self): ...
...
>>> class Car(Vehicle):
...     pass
...
>>> class Truck(Vehicle):
...     pass
...
>>> class Motorbike(Vehicle):
...     pass
...
...
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()
>>>
>>> yamaha = Motorbike()
>>> yamaha.engine_start()
>>> yamaha.engine_stop()
>>> yamaha.window_open()  # motorbikes don't have windows
>>> yamaha.window_close()  # motorbikes don't have windows

Solution 1 - code duplication:

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
>>>
>>> class Car(Vehicle):
...     def window_open(self): ...
...     def window_close(self): ...
>>>
>>> class Truck(Vehicle):
...     def window_open(self): ...
...     def window_close(self): ...
>>>
>>> class Motorbike(Vehicle):
...     pass
>>>
>>>
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()
>>>
>>> yamaha = Motorbike()
>>> yamaha.engine_start()
>>> yamaha.engine_stop()

Solution 2 - not implemented:

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
...     def window_open(self): ...
...     def window_close(self): ...
>>>
>>> class Car(Vehicle):
...     pass
>>>
>>> class Truck(Vehicle):
...     pass
>>>
>>> class Motorbike(Vehicle):
...     def window_open(self): raise NotImplementedError
...     def window_close(self): raise NotImplementedError
>>>
>>>
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()
>>>
>>> yamaha = Motorbike()
>>> yamaha.engine_start()
>>> yamaha.engine_stop()
>>> yamaha.window_open()
Traceback (most recent call last):
NotImplementedError
>>> yamaha.window_close()
Traceback (most recent call last):
NotImplementedError

16.22.4. Multilevel Inheritance¶

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
>>>
>>> class VehicleWithWindows(Vehicle):
...     def window_open(self): ...
...     def window_close(self): ...
>>>
>>> class Car(VehicleWithWindows):
...     pass
>>>
>>> class Truck(VehicleWithWindows):
...     pass
>>>
>>> class Motorbike(Vehicle):
...     pass
>>>
>>>
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()
>>>
>>> yamaha = Motorbike()
>>> yamaha.engine_start()
>>> yamaha.engine_stop()

Problem - Passenger take/drop: (let's assume that Truck cannot take passengers)

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
>>>
>>> class VehicleWithWindows(Vehicle):
...     def window_open(self): ...
...     def window_close(self): ...
>>>
>>> class Car(VehicleWithWindows):
...     def passenger_take(self): ...
...     def passenger_drop(self): ...
>>>
>>> class Truck(VehicleWithWindows):
...     pass
>>>
>>> class Motorbike(Vehicle):
...     def passenger_take(self): ...
...     def passenger_drop(self): ...
>>>
>>>
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()
>>>
>>> yamaha = Motorbike()
>>> yamaha.engine_start()
>>> yamaha.engine_stop()

16.22.5. Multilevel Inheritance¶

>>> class Vehicle:
...     def engine_start(self): ...
...     def engine_stop(self): ...
>>>
>>> class VehicleWithWindows(Vehicle):
...     def window_open(self): ...
...     def window_close(self): ...
>>>
>>> class VehicleWithPassengers(Vehicle):
...     def passenger_take(self): ...
...     def passenger_drop(self): ...
>>>
>>> class Car(VehicleWithWindows, VehicleWithPassengers):
...     pass
>>>
>>> class Truck(VehicleWithWindows):
...     pass
>>>
>>> class Motorbike(VehicleWithPassengers):
...     pass
>>>
>>>
>>>
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>> maluch.passenger_take()
>>> maluch.passenger_drop()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()
>>>
>>> yamaha = Motorbike()
>>> yamaha.engine_start()
>>> yamaha.engine_stop()
>>> yamaha.passenger_take()
>>> yamaha.passenger_drop()

16.22.6. Mixin Classes¶

>>> class Vehicle:
...     pass
>>>
>>> class HasEngine:
...     def engine_start(self): ...
...     def engine_stop(self): ...
>>>
>>> class HasWindows:
...     def window_open(self): ...
...     def window_close(self): ...
>>>
>>> class HasPassengers:
...     def passenger_take(self): ...
...     def passenger_drop(self): ...
>>>
>>>
>>> class Car(Vehicle, HasEngine, HasWindows, HasPassengers):
...     pass
>>>
>>> class Truck(Vehicle, HasEngine, HasWindows):
...     pass
>>>
>>> class Motorbike(Vehicle, HasEngine, HasPassengers):
...     pass
>>>
>>>
>>> maluch = Car()
>>> maluch.engine_start()
>>> maluch.engine_stop()
>>> maluch.window_open()
>>> maluch.window_close()
>>> maluch.passenger_take()
>>> maluch.passenger_drop()
>>>
>>> scania = Truck()
>>> scania.engine_start()
>>> scania.engine_stop()
>>> scania.window_open()
>>> scania.window_close()
>>>
>>> yamaha = Motorbike()
>>> yamaha.engine_start()
>>> yamaha.engine_stop()
>>> yamaha.passenger_take()
>>> yamaha.passenger_drop()

16.22.7. Use Case - 0x01¶

>>> class User:
...     pass
>>>
>>> class Admin:
...     pass
>>>
>>>
>>> mark = User()
>>> isinstance(mark, User)
True
>>> isinstance(mark, Admin)
False
>>>
>>>
>>> melissa = Admin()
>>> isinstance(melissa, User)
False
>>> isinstance(melissa, Admin)
True

Single Inheritance:

>>> class User:
...     pass
...
>>> class Admin(User):
...     pass
...
...
>>> mark = User()
>>> isinstance(mark, User)
True
>>> isinstance(mark, Admin)
False
>>>
>>>
>>> melissa = Admin()
>>> isinstance(melissa, User)
True
>>> isinstance(melissa, Admin)
True

Multilevel Inheritance:

>>> class User:
...     pass
...
>>> class Admin(User):
...     pass
...
>>> class SuperAdmin(Admin):
...     pass
>>>
>>>
>>> mark = User()
>>> isinstance(mark, User)
True
>>> isinstance(mark, Admin)
False
>>> isinstance(mark, SuperAdmin)
False
>>>
>>>
>>> melissa = Admin()
>>> isinstance(melissa, User)
True
>>> isinstance(melissa, Admin)
True
>>> isinstance(melissa, SuperAdmin)
False
>>>
>>>
>>> rick = SuperAdmin()
>>> isinstance(rick, User)
True
>>> isinstance(rick, Admin)
True
>>> isinstance(rick, SuperAdmin)
True

Multiple Inheritance:

>>> class CanEditSelf:
...     pass
>>>
>>> class CanEditUsers:
...     pass
>>>
>>> class CanEditAdmins:
...     pass
>>>
>>>
>>> class Account:
...     pass
>>>
>>> class User(Account, CanEditSelf):
...     pass
>>>
>>> class Admin(Account, CanEditSelf, CanEditUsers):
...     pass
>>>
>>> class SuperAdmin(Account, CanEditSelf, CanEditUsers, CanEditAdmins):
...     pass

16.22.8. Assignments¶

Code 16.28. Solution¶

"""
* Assignment: OOP InheritancePatterns NoInheritance
* Complexity: easy
* Lines of code: 8 lines
* Time: 3 min

English:
    1. Create classes `Account`, `User`
    2. Do not use inheritance
    3. Assignment demonstrates syntax, so do not add any attributes and methods
    4. Run doctests - all must succeed

Polish:
    1. Stwórz klasy `Account`, `User`
    2. Nie używaj dziedziczenia
    3. Zadanie demonstruje składnię, nie dodawaj żadnych atrybutów i metod
    4. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isclass

    >>> assert isclass(Account)
    >>> assert isclass(User)
    >>> assert not issubclass(Account, User)
    >>> assert not issubclass(User, Account)

    >>> assert len(Account.__subclasses__()) == 0
    >>> assert len(User.__subclasses__()) == 0
"""

Code 16.29. Solution¶

"""
* Assignment: OOP InheritancePatterns Simple
* Type: class assignment
* Complexity: easy
* Lines of code: 4 lines
* Time: 3 min

English:
    1. Create class `Account`
    2. Create class `User` which inherits from `Account`
    3. Run doctests - all must succeed

Polish:
    1. Stwórz klasę `Account`
    2. Stwórz klasę `User`, która dziedziczy po `Account`
    3. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isclass

    >>> assert isclass(Account)
    >>> assert isclass(User)
    >>> assert issubclass(Account, object)
    >>> assert issubclass(User, object)
    >>> assert issubclass(User, Account)
    >>> assert not issubclass(Account, User)

    >>> assert len(Account.__subclasses__()) == 1
    >>> assert len(User.__subclasses__()) == 0
"""

Code 16.30. Solution¶

"""
* Assignment: OOP InheritancePatterns Multilevel
* Complexity: easy
* Lines of code: 8 lines
* Time: 3 min

English:
    1. Create class `Account`
    2. Create class `User` which inherits from `Account`
    2. Create class `Admin` which inherits from `User`
    3. Run doctests - all must succeed

Polish:
    1. Stwórz klasę `Account`
    2. Stwórz klasę `User`, która dziedziczy po `Account`
    2. Stwórz klasę `Admin`, która dziedziczy po `User`
    3. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isclass

    >>> assert isclass(Account)
    >>> assert isclass(User)
    >>> assert isclass(Admin)

    >>> assert issubclass(Account, object)
    >>> assert issubclass(User, object)
    >>> assert issubclass(User, Account)
    >>> assert issubclass(Admin, object)
    >>> assert issubclass(Admin, User)
    >>> assert issubclass(Admin, Account)

    >>> assert not issubclass(User, Admin)
    >>> assert not issubclass(Account, User)
    >>> assert not issubclass(Account, Admin)

    >>> assert len(Account.__subclasses__()) == 1
    >>> assert len(User.__subclasses__()) == 1
    >>> assert len(Admin.__subclasses__()) == 0
"""

# Create class `Account`
# Create class `User` which inherits from `Account`
# Create class `Admin` which inherits from `User`