Abstract Classes & Interfaces

from abc import ABC, abstractmethod

class PaymentProcessor(ABC):
    @abstractmethod
    def process(self, amount):
        pass
    
    @abstractmethod
    def refund(self, amount):
        pass
    
    def log(self, message):  # Concrete method
        print(f"  LOG: {message}")

class CreditCard(PaymentProcessor):
    def process(self, amount):
        self.log(f"Credit card charge: ${amount}")
        return True
    
    def refund(self, amount):
        self.log(f"Credit card refund: ${amount}")
        return True

class PayPal(PaymentProcessor):
    def process(self, amount):
        self.log(f"PayPal payment: ${amount}")
        return True
    
    def refund(self, amount):
        self.log(f"PayPal refund: ${amount}")
        return True

# Can't instantiate abstract class
# p = PaymentProcessor()  # TypeError!

# Must implement ALL abstract methods
processors = [CreditCard(), PayPal()]
for p in processors:
    p.process(99.99)
    print(f"  Is PaymentProcessor? {isinstance(p, PaymentProcessor)}")