3.16. OOP Abstract Polymorphism¶
3.16.1. SetUp¶
>>> from abc import ABCMeta, abstractmethod
3.16.2. Procedural Polymorphism¶
UNIX
getchar()function used function lookup table with pointers
>>> keyboard = {
... 'open': lambda: ...,
... 'close': lambda: ...,
... 'read': lambda bytes: ...,
... 'write': lambda content: ...,
... 'seek': lambda position: ...,
... }
>>>
>>> file = {
... 'open': lambda: ...,
... 'close': lambda: ...,
... 'read': lambda bytes: ...,
... 'write': lambda content: ...,
... 'seek': lambda position: ...,
... }
>>>
>>> socket = {
... 'open': lambda: ...,
... 'close': lambda: ...,
... 'read': lambda bytes: ...,
... 'write': lambda content: ...,
... 'seek': lambda position: ...,
... }
>>>
>>>
>>> def getchar(obj):
... obj['open']()
... obj['seek'](0)
... obj['read'](1)
... obj['close']()
>>>
>>>
>>> getchar(file)
>>> getchar(keyboard)
>>> getchar(socket)
3.16.3. Elif¶
It all starts with single if statement
>>> language = 'English'
>>>
>>> if language == 'English':
... result = 'Hello'
>>>
>>> print(result)
Hello
>>> language = 'English'
>>>
>>> if language == 'English':
... result = 'Hello'
... elif language == 'Polish':
... result = 'Witaj'
>>>
>>> print(result)
Hello
It quickly grows into multiple elif:
>>> language = 'English'
>>>
>>> if language == 'English':
... result = 'Hello'
... elif language == 'Polish':
... result = 'Witaj'
... elif language == 'Spanish':
... result = 'Hola'
... else:
... result = 'Unknown language'
>>>
>>> print(result)
Hello
3.16.4. Match: Switch Pattern¶
Since Python 3.10: PEP 636 -- Structural Pattern Matching: Tutorial
More information Match About [1]
In other languages you may find switch statement. Since Python 3.10
there is a match statement which can do the similar thing:
>>> language = 'English'
>>>
>>> match language:
... case 'English': result = 'Hello'
... case 'Polish': result = 'Witaj'
... case 'Spanish': result = 'Hola'
... case _: result = 'Unknown language'
Problem is that, match moves business logic to the execution place.
You can write it in a function using dict and .get() method with
default value. It's a bit cleaner, but essentially the same...
>>> def switch(key):
... return {
... 'English': 'Hello',
... 'Polish': 'Witaj',
... 'Spanish': 'Hola',
... }.get(key, 'Unknown language')
>>>
>>> switch('English')
'Hello'
>>> switch('Spanish')
'Hola'
3.16.5. Polymorphism¶
>>> class UIElement(metaclass=ABCMeta):
... def __init__(self, name):
... self.name = name
...
... @abstractmethod
... def render(self):
... pass
>>>
>>>
>>> def render(component: list[UIElement]):
... for element in component:
... element.render()
>>> class TextInput(UIElement):
... def render(self):
... print(f'Rendering {self.name} TextInput')
>>>
>>>
>>> class Button(UIElement):
... def render(self):
... print(f'Rendering {self.name} Button')
>>> login_window = [
... TextInput(name='Username'),
... TextInput(name='Password'),
... Button(name='Submit'),
... ]
>>>
>>> render(login_window)
Rendering Username TextInput
Rendering Password TextInput
Rendering Submit Button
3.16.6. Use Case - 0x01¶
>>> from abc import ABCMeta, abstractmethod
>>> from dataclasses import dataclass
>>>
>>>
>>> @dataclass
... class Person(metaclass=ABCMeta):
... name: str
...
... @abstractmethod
... def say_hello(self):
... pass
>>>
>>>
>>> class Astronaut(Person):
... def say_hello(self):
... return f'Hello {self.name}'
>>>
>>> class Cosmonaut(Person):
... def say_hello(self):
... return f'Witaj {self.name}'
>>>
>>>
>>> def hello(crew: list[Person]) -> None:
... for member in crew:
... print(member.say_hello())
>>>
>>>
>>> crew = [Astronaut('Mark Watney'),
... Cosmonaut('José Jiménez'),
... Astronaut('Melissa Lewis'),
... Cosmonaut('Pan Twardowski'),
... ]
>>>
>>> hello(crew)
Hello Mark Watney
Witaj José Jiménez
Hello Melissa Lewis
Witaj Pan Twardowski
In Python, due to the duck typing and dynamic nature of the language, the Interface or abstract class is not needed to do polymorphism:
>>> from dataclasses import dataclass
>>>
>>>
>>> @dataclass
... class Astronaut:
... name: str
...
... def say_hello(self):
... return f'Hello {self.name}'
>>>
>>> @dataclass
... class Cosmonaut:
... name: str
...
... def say_hello(self):
... return f'Witaj {self.name}'
>>>
>>>
>>> crew = [Astronaut('Mark Watney'),
... Cosmonaut('José Jiménez'),
... Astronaut('Melissa Lewis'),
... Cosmonaut('Pan Twardowski'),
... ]
>>>
>>> for member in crew:
... print(member.say_hello())
Hello Mark Watney
Witaj José Jiménez
Hello Melissa Lewis
Witaj Pan Twardowski
3.16.7. Use Case - 0x02¶
Login Window
>>> import re
>>>
>>>
>>> class UIElement:
... def __init__(self, name):
... self.name = name
...
... def on_mouse_hover(self):
... raise NotImplementedError
...
... def on_mouse_out(self):
... raise NotImplementedError
...
... def on_mouse_click(self):
... raise NotImplementedError
...
... def on_key_press(self):
... raise NotImplementedError
...
... def render(self):
... raise NotImplementedError
>>>
>>>
>>> class Button(UIElement):
... action: str
...
... def __init__(self, *args, action: str | None = None, **kwargs):
... self.action = action
... super().__init__(*args, **kwargs)
...
... def on_key_press(self):
... pass
...
... def on_mouse_hover(self):
... pass
...
... def on_mouse_out(self):
... pass
...
... def on_mouse_click(self):
... pass
...
... def render(self):
... action = self.action
... print(f'Rendering Button with {action}')
>>>
>>>
>>> class Input(UIElement):
... regex: re.Pattern
...
... def __init__(self, *args, regex: str | None = None, **kwargs):
... self.regex = re.compile(regex)
... super().__init__(*args, **kwargs)
...
... def on_key_press(self):
... pass
...
... def on_mouse_hover(self):
... pass
...
... def on_mouse_out(self):
... pass
...
... def on_mouse_click(self):
... pass
...
... def render(self):
... regex = self.regex
... print(f'Rendering Input with {regex}')
>>>
>>>
>>> def render(components: list[UIElement]):
... for obj in components:
... obj.render()
>>>
>>>
>>> login_window = [
... Input('Username', regex='[a-zA-Z0-9]'),
... Input('Password', regex='[a-zA-Z0-9!@#$%^&*()]'),
... Button('Submit', action='/login.html'),
... ]
>>>
>>> render(login_window)
Rendering Input with re.compile('[a-zA-Z0-9]')
Rendering Input with re.compile('[a-zA-Z0-9!@#$%^&*()]')
Rendering Button with /login.html