3.1. OOP Principles¶
Encapsulation
Abstraction
Inheritance
Polymorphism
3.1.1. Encapsulation¶
Do not allow to modify attributes directly
Hide them behind setters and getters
Prevents objects to get to an invalid state
>>> position_x = 0
>>> position_y = 0
>>>
>>> def position_set(x, y):
... global position_x
... global position_y
... position_x = x
... position_y = y
>>>
>>> def position_get():
... return position_x, position_y
>>>
>>> position_set(1, 2)
>>> position_get()
(1, 2)
>>> class Position:
... x: int = 0
... y: int = 0
...
... def set(self, x, y):
... self.x = x
... self.y = y
...
... def get(self):
... return self.x, self.y
>>>
>>> position = Position()
>>> position.set(1, 2)
>>> position.get()
(1, 2)
3.1.2. Abstraction¶
Reduce complexity by hiding unnecessary details
User do not need what does it mean to send email, that you have to connect, auth and later disconnect
>>> class MarsMission:
... def send_astronauts(self, astronauts):
... self._develop_tools()
... self._develop_rocket()
... self._train_crew(astronauts)
... self._launch_rocket()
... self._navigate_in_space()
... self._land()
... self._first_step_on_mars(astronauts)
...
... def _develop_tools(self):
... print('Developing Tools')
...
... def _develop_rocket(self):
... print('Developing Rocket')
...
... def _train_crew(self, astronauts):
... print('Training Crew')
...
... def _launch_rocket(self):
... print('Launch Rocket')
...
... def _navigate_in_space(self):
... print('Navigate in space')
...
... def _land(self):
... print('Entry, descend and landing')
...
... def _first_step_on_mars(self, astronauts):
... print('First step on Mars')
>>>
>>>
>>> mars = MarsMission()
>>> mars.send_astronauts(['Mark Watney', 'Melissa Lewis', ...])
Developing Tools
Developing Rocket
Training Crew
Launch Rocket
Navigate in space
Entry, descend and landing
First step on Mars
3.1.3. Inheritance¶
>>> class Person:
... firstname: str
... lastname: str
...
... def say_hello(self):
... print(f'Hello {self.firstname} {self.lastname}')
>>>
>>>
>>> class Astronaut(Person):
... pass
>>>
>>>
>>> astro = Astronaut()
>>> astro.firstname = 'Mark'
>>> astro.lastname = 'Watney'
>>> astro.say_hello()
Hello Mark Watney
3.1.4. Polymorphism¶
Ability of an object to take many forms
>>> class Person:
... def __init__(self, name):
... self.name = name
...
... 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'Привет {self.name}'
>>>
>>>
>>> def hello(crew: list[Person]) -> None:
... for member in crew:
... print(member.say_hello())
>>>
>>>
>>> crew = [Astronaut('Mark Watney'),
... Cosmonaut('Иван Иванович'),
... Astronaut('Melissa Lewis'),
... Cosmonaut('Pan Twardowski')]
>>>
>>> hello(crew)
Hello Mark Watney
Привет Иван Иванович
Hello Melissa Lewis
Привет Pan Twardowski