Create interfaces and enforce contracts.

Basic ABC

```python from abc import ABC, abstractmethod

class Animal(ABC): @abstractmethod def speak(self): pass @abstractmethod def move(self): pass

class Dog(Animal): def speak(self): return "Woof!" def move(self): return "Running"

dog = Dog() print(dog.speak()) # Woof!

animal = Animal() # Error! Can't instantiate ```

Abstract Properties

```python from abc import ABC, abstractmethod

class Shape(ABC): @property @abstractmethod def area(self): pass

class Rectangle(Shape): def __init__(self, width, height): self.width = width self.height = height @property def area(self): return self.width * self.height

rect = Rectangle(10, 20) print(rect.area) # 200 ```

Multiple Abstract Methods

```python from abc import ABC, abstractmethod

class Database(ABC): @abstractmethod def connect(self): pass @abstractmethod def disconnect(self): pass @abstractmethod def query(self, sql): pass

class PostgreSQL(Database): def connect(self): print("Connected to PostgreSQL") def disconnect(self): print("Disconnected") def query(self, sql): print(f"Running: {sql}")

db = PostgreSQL() db.connect() db.query("SELECT * FROM users") ```

Check Subclass

```python from abc import ABC

class Vehicle(ABC): pass

class Car(Vehicle): pass

print(issubclass(Car, Vehicle)) # True print(isinstance(Car(), Vehicle)) # True ```

Remember

- Use ABC for interfaces - Abstract methods must be implemented - Can't instantiate abstract classes