Introduction 🌟
An **Abstract Base Class (ABC)** in Python is a class that cannot be instantiated and is used to define a **blueprint** for other classes. ABCs ensure that child classes implement certain required methods. This is essential for building **structured, maintainable, and scalable** applications.
Note
💡 They contain one or more abstract methods
💡 Child classes must implement these abstract methods
1. Importing the ABC Tools 🧱
import_abc.py
from abc import ABC, abstractmethod✔ ABC → Base class to define an abstract class
✔ @abstractmethod → Marks methods that must be overridden
2. Creating a Simple Abstract Base Class 🎨
simple_abc.py
from abc import ABC, abstractmethod
class Animal(ABC):
@abstractmethod
def sound(self):
pass
# a = Animal() # ❌ Error: Can't instantiate abstract class✔ ABC cannot be instantiated
✔ Abstract method must be implemented in child class
3. Implementing Abstract Methods in Child Classes 🐾
child_implement.py
class Dog(Animal):
def sound(self):
return "Bark"
class Cat(Animal):
def sound(self):
return "Meow"
d = Dog()
print(d.sound())✔ Every subclass must implement sound()
✔ Failure → TypeError at runtime
4. Abstract Base Class with Constructor 🚀
abc_constructor.py
from abc import ABC, abstractmethod
class Shape(ABC):
def __init__(self, color):
self.color = color
@abstractmethod
def area(self):
pass
class Square(Shape):
def __init__(self, side, color):
super().__init__(color)
self.side = side
def area(self):
return self.side * self.side
s = Square(5, "blue")
print(s.area())✔ ABCs can have regular methods and constructors
✔ Child classes must call parent constructor using super()
5. ABC with Multiple Abstract Methods 📚
multiple_methods.py
class Vehicle(ABC):
@abstractmethod
def start(self): pass
@abstractmethod
def stop(self): pass
class Car(Vehicle):
def start(self):
print("Car starting")
def stop(self):
print("Car stopping")
c = Car()
c.start()
c.stop()✔ All abstract methods must be implemented
6. Partially Abstract Classes (Concrete + Abstract) ⚡
partial_abstract_class.py
class Device(ABC):
def info(self):
print("Device info")
@abstractmethod
def run(self):
pass
class Laptop(Device):
def run(self):
print("Laptop running")
l = Laptop()
l.info()
l.run()✔ ABCs can contain both abstract and non-abstract methods
✔ Useful for shared logic across subclasses
7. Real-World Example — Payment System 💳
payment_abc.py
class Payment(ABC):
@abstractmethod
def pay(self, amount): pass
class Cash(Payment):
def pay(self, amount):
print(f"Paid {amount} in cash")
class Card(Payment):
def pay(self, amount):
print(f"Paid {amount} using card")
p = Card()
p.pay(500)8. Abstract Properties & Abstract Class Methods 🧠
abstract_property.py
class Product(ABC):
@property
@abstractmethod
def price(self):
pass
class Item(Product):
@property
def price(self):
return 500
i = Item()
print(i.price)✔ Even properties can be abstract and must be overridden
9. Abstract Class with Static Method 🧩
abstract_staticmethod.py
class Tool(ABC):
@staticmethod
@abstractmethod
def info():
pass
class Hammer(Tool):
@staticmethod
def info():
return "Hammer tool"
print(Hammer.info())✔ Abstract static methods must also be implemented
10. Why Use Abstract Base Classes? 🎯
- ✔ Enforces consistency across subclasses
- ✔ Defines a common interface for all child classes
- ✔ Organizes code into clear structures
- ✔ Prevents incomplete implementations
- ✔ Promotes clean, scalable system architecture
11. ABC vs Interface (in other languages) ⚔️
| Abstract Base Class | Interface (Java/C#) |
|---|---|
| Can have constructors | Cannot have constructors |
| Can have concrete methods | Only method signatures |
| Supports attributes | No attributes |
| Used via abc module | Built-in language feature |
12. Best Practices 💡
- ✔ Use ABCs when multiple subclasses share a required structure
- ✔ Keep abstract methods descriptive
- ✔ Avoid adding unnecessary abstract methods
- ✔ Use regular methods inside ABC for shared code
- ✔ Use ABCs to define clean interfaces in large applications
Conclusion 🎉
You now fully understand Abstract Base Classes in Python! Want the next topic? Try Interfaces, Magic Methods, Abstract Properties, or MRO. Just tell me! 😊