Interfaces in Python

Interfaces in Python : Implementing Abstract Base Classes

In Python, an interface is a collection of abstract methods. Python does not have a native support for interfaces, but we can use Abstract Base Classes to create interfaces in Python.

An interface is like a contract. It defines the syntax that any class must follow to implement that interface. An interface is like a blueprint for a class. If a class follows the blueprint, it is guaranteed to provide the necessary functionality.

Abstract Base Classes

Python comes with a module which provides the infrastructure for defining Abstract Base Classes (ABCs). The module is called abc. ABCs allow you to define a set of methods that must be implemented by the derived classes.

To create an interface in Python, you can create an abstract class using the abc module. The abstract class can have abstract methods that must be implemented by the derived classes.

Here is an example of an interface in Python using the abc module:

interfaces.py

from abc import ABC, abstractmethod
 
class Shape(ABC):
    @abstractmethod
    def area(self):
        pass
 
    @abstractmethod
    def perimeter(self):
        pass

In the above example, we have created an interface called Shape. The Shape interface has two abstract methods area and perimeter. Any class that implements the Shape interface must provide the implementation for these two methods.

Here is an example of a class that implements the Shape interface:

rectangle.py

from interfaces import Shape
 
class Rectangle(Shape):
    def __init__(self, width, height):
        self.width = width
        self.height = height
 
    def area(self):
        return self.width * self.height
 
    def perimeter(self):
        return 2 * (self.width + self.height)

In the above example, we have created a class called Rectangle that implements the Shape interface. The Rectangle class provides the implementation for the area and perimeter methods.

Here is an example of a class that does not implement the Shape interface:

circle.py

class Circle:
    def __init__(self, radius):
        self.radius = radius
 
    def area(self):
        return 3.14 * self.radius * self.radius
 
    def perimeter(self):
        return 2 * 3.14 * self.radius

In the above example, we have created a class called Circle that does not implement the Shape interface. The Circle class provides the implementation for the area and perimeter methods, but it does not implement the Shape interface.

diagram Interfaces in Python mermaid

  classDiagram
    class Shape {
        + area()
        + perimeter()
    }
    class Rectangle {
        - width
        - height
        + area()
        + perimeter()
    }
    class Circle {
        - radius
        + area()
        + perimeter()
    }
    Shape <|-- Rectangle

Interfaces in Python

In this example, we have created an interface called Shape with two abstract methods area and perimeter. We have created a class called Rectangle that implements the Shape interface. We have also created a class called Circle that does not implement the Shape interface.

Calling Interface Methods

You can call the interface methods using the object of the class that implements the interface. Here is an example:

main.py

from rectangle import Rectangle
 
r = Rectangle(5, 10)
print("Area:", r.area())
print("Perimeter:", r.perimeter())

Output:

Command

C:\Users\username\Desktop> python main.py
Area: 50
Perimeter: 30

In this example, we have created an object of the Rectangle class and called the area and perimeter methods. The Rectangle class implements the Shape interface, so it provides the implementation for the area and perimeter methods.

You can create an object of the Abstract Base Class, but you cannot call the abstract methods using the object of the Abstract Base Class. You must create a derived class and then call the abstract methods using the object of the derived class.

If you try to call the abstract methods using the object of the Abstract Base Class, you will get an error.

main.py

from interfaces import Shape
 
s = Shape()
print("Area:", s.area())
print("Perimeter:", s.perimeter())

Output:

Error

C:\Users\username\Desktop> python main.py
TypeError: Can't instantiate abstract class Shape with abstract methods area, perimeter

In this example, we have created an object of the Shape interface and tried to call the area and perimeter methods. Since the Shape interface is an abstract class, we cannot create an object of the Shape interface, and we cannot call the area and perimeter methods using the object of the Shape interface.

Conclusion

In Python, an interface is a collection of abstract methods. Python does not have a native support for interfaces, but we can use Abstract Base Classes to create interfaces in Python. An interface is like a contract. It defines the syntax that any class must follow to implement that interface. An interface is like a blueprint for a class. For more information, you can refer to the official documentation of the abc module. For more tutorials, you can visit the Python Central Hub.

Interfaces in Python