Python OOP (Classes, Init, Inheritance)

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Python OOP

Splitting a larger task into smaller pieces.

Classes are blueprints (attributes + methods) to build objects

# A potential blueprint for a waiter (an object)
 
class WaiterBlueprint:
    # attributes (variables) are:
    is_holding_plate = True
    tables = [4, 5, 6]
 
    # methods (functions) are:
    def take_order():
        ...
    def handle_payments():
        ...
 
# this whole code serves as a blueprint, which makes it a class
 
waiter = WaiterBlueprint()
# Pascal case for each word, no underscores
# The parenthesis is just to construct an object.

Getting attributes and methods from an object

car.speed
car.weight
# where car is the object, and speed/weight are variables.
 
car.stop()
# where car is the object, and stop() is a function

Make objects and play with them

car = CarBlueprint()
 
print(car.speed)   # using attributes (variables)
car.move()         # using methods (functions)

Prevent “indent expected” error

class MyClass:
    pass

Initialising using constructors

__init__ function

Set variables, counters, etc., to their starting values when an object is being initialised.

class Car:
    def __init__(self):
        print("new user being created")
 
# init function is going to be called everytime you construct an object from this class.

Setting attributes

# SELF is just the OBJECT that will be made
 
class Car:
    def __init__(self, seats, windows):    # PARAMETERS
        self.chair = seats                 # ARGUMENTS
        self.windows = windows
 
# always have the SELF parameter, which is the actual object being created.
# name of attribute does not need to match parameter name, but should.
 
my_car = Car(5, 6)
# always pass in the argument for the additional parameters in our init function.
 
 
# the longer tedious method would be:
class Car:
    pass
 
my_car = Car()
my_car.chair = 5
my_car.windows = 6

Default attribute values

class User:
    def __init__(self, user_id):
        self.id = user_id
        self.followers = 0
 
user_1 = User("001")
print(user_1.followers)   # gives you 0

Setting methods

class Car:
    def enter_race_mode(self):
        self.seats = 2
 
my_car.enter_race_mode()
 
# another example
 
class User:
    def __init__(self):
        self.following = 0
 
    def follow(self, user):
        user.following += 1
        self.following += 1
 
user_1 = User()
user_2 = User()
 
user_1.follow(user_2)
 
# both user's following attribute is now 1.

Class inheritance

Inheriting attributes and methods between different classes.

Inheriting the initialization

class Fish(Animal):
    def __init__(self):
        super().__init__()
 
# inheriting a fish class from the animal class
# for example
 
class Animal:
 
    def __init__(self):
        self.num_eyes = 2
 
    def breathe(self):
        print("Inhale, Exhale")
 
 
class Fish(Animal):
 
    def __init__(self):
        super().__init__()
    # taking something from the Animal class
 
    def breathe(self):
        super().breathe()
        print("while in water")
    # taking something from the Animal class and building on it!
 
    def swim(self):
        print("Moving in water")

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