Dependency Injection Pattern

Definition

It is a way of using Objects of other Classes by creating an object externally and passing it as an argument.

Example

class Weapon:
    def __init__(self, name):
        self.name = name
 
class Player:
    def __init__(self, name, weapon):    # weapon argument is added as a placeholder
        self.name = name
        self.weapon = weapon
 
    def attack(self):
        print(f"{self.name} attacks with {self.weapon.name}!")
 
# We create the weapon externally
player_weapon = Weapon("Bow")
 
# We inject the weapon into the Player class
player = Player("Archer", player_weapon)
player.attack()

Without Dependency Interjection

class Weapon:
    def __init__(self, name):
        self.name = name
 
class Player:
    def __init__(self, name):
        self.name = name
        self.weapon = Weapon("Sword")    # Player class depends on Weapon()
 
    def attack(self):
        print(f"{self.name} attacks with {self.weapon.name}!")
        
player = Player("Hero")
player.attack()