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Object Oriented

Object Oriented Python#

Everything in python is an Object

  • Usually 1 class per file


    class Monster:
        hit_points = 1
        color = 'yellow'
        weapon = 'sword'

importing a class#

from monster import Monster - means bring Monster class from inside the monster library

Every file is a library

Using attributes#

eg. Monster.hit_points

Creating an instance of a class#

Use ()

eg. jubjub = Monster()


Functions that are part of a class are called methods

Every method at the very least takes the self argument

Eg. def battlecry(self):

self always represents the instance you are calling the method on (doesn’t have to be called self)

Can use self variable to get info about the current instance

Dunder Init (init)#

Runs when a new instance is created

a pythonic construcutor


    class Monster:
        def __init__(self, hit_points, weapon, color, sound):
            self.hit_points = hit_points
            self.weapon = weapon
            self.color = color
            self.sound = sound

        def battlecry(self):
            return self.sound.upper()

    slimey = Monster(5, 'Sword', 'blue', 'GLUG')

Can set defaults:

    def __init__(self, hit_points=5, weapon='Sword', color='yellow', sound='roar'):

Or dictionary unpacking:

** means handle as dictionary

    def __init__(self, **kwargs):
        self.hit_points = kwargs.get('hit_points', 1)
        # Can still set the default

Delete an instance#

    jubjub = Monster()
    del jubjub

Setting attributes#

Usually used in __init__(self, **kwargs)

   for key, value in kwargs.items():
        setattr(self, key, value)

Usage: jabber = Monster(color='blue', hit_points=500, sound='whiffling', adjective='manxsome')


Showing a subclass = Inheriting all attribute of parent class:

    class Goblin(Monster):

Every class inherits from default object class

so class Monster: === class Monster(objecy)

pass keyword tells python to keep going as though nothing has happened


__str__ a magic method called when class is converted to a string / string representation

self.__class__.__name__ - class name and string representation of that class

    def __str__(self):
        return '{} {}, HP: {}, XP: {}'.format(self.color.title(),

    from monster import Monster
    my_mon = Monster()

Will print the dunder str


Don’t repeat yourself

  • group common operations into Functions
  • group common functionality into classes


You can override an inherited class simply by writing the method in the subclass


Special variable only ever equa to itself

It is falsey

sys.exit()..sys is a library to exit the interpreter