3.1. OOP Principles¶
3.1.1. Rationale¶
Encapsulation
Abstraction
Inheritance
Polymorphism
3.1.2. 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)
3.1.3. 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
3.1.4. 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
3.1.5. 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('Jan Twardowski')]
>>>
>>> hello(crew)
Hello Mark Watney
Привет Иван Иванович
Hello Melissa Lewis
Привет Jan Twardowski