What are ABC (Abstract Base Classes)?

Question

Accepted Answer

**ABC** — abstract classes for **defining interfaces**.

```python
from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self) -> float:
        pass

@abstractmethod
    def perimeter(self) -> float:
        pass

def describe(self) -> str:
        return f"Area: {self.area():.2f}"

class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius

def area(self) -> float:
        return 3.14 * self.radius ** 2

def perimeter(self) -> float:
        return 2 * 3.14 * self.radius

# shape = Shape()  # Error! Cannot instantiate
circle = Circle(5)
print(circle.describe())  # "Area: 78.50"

# Type checking
print(isinstance(circle, Shape))  # True
print(issubclass(Circle, Shape))  # True
```

**When to use:**
- Defining interfaces.
- Enforcing method implementation.
- isinstance checks.

Python: What are ABC (Abstract Base Classes)?