python inner class

An inner class, also known as a nested class, is a class that’s defined within the scope of another class. When an object is instantiated from an outer class, the object inside the nested class can also be used. It’s possible for a class to contain multiple nested classes, though they’re often used sparingly.

Python’s ability to nest classes within other classes is one of its many versatile features. A nested class inherits all attributes and methods from its enclosing class.

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Inner Class in Python: A Simple Example

In Python, inner classes or nested classes can be defined inside the scope of another class. These inner classes can access all the members of their enclosing class.

Proper indentation is crucial when defining inner classes. Typically, each inner class is indented by 4 spaces to adhere to PEP 8, Python’s style guide.

Below is an example where we define a Human class with a nested Head class. We then create an instance of the Human class and call a method from the nested Head class:

#!/usr/bin/env python

class Human:
    def __init__(self):
        self.name = 'Guido'
        self.head = self.Head()
  
    class Head:
        def talk(self):
            return 'talking...'
  
if __name__ == '__main__':
    guido = Human()
    print(guido.name)
    print(guido.head.talk())

Output:

Guido
talking...

In the example above, the inner Head class possesses its own method. Inner classes can encapsulate both methods and variables. The constructor of the Human class (__init__) initializes a new head object.

Multiple Inner Classes in Python

Python doesn’t impose a limitation on the number of inner classes. Here’s an example that includes two nested classes within the Human class:

#!/usr/bin/env python

class Human:
    def __init__(self):
        self.name = 'Guido'
        self.head = self.Head()
        self.brain = self.Brain()
  
    class Head:
        def talk(self):
            return 'talking...'

    class Brain:
        def think(self):
            return 'thinking...'
  
if __name__ == '__main__':
    guido = Human()
    print(guido.name)
    print(guido.head.talk())
    print(guido.brain.think())

Utilizing inner classes allows for more organized and object-oriented code. A single outer object can comprise multiple sub-objects, enabling a more structured programming approach.

Benefits of Using Inner Classes

Grouping classes within other classes through the use of inner classes can offer several benefits:

1. Inner classes are confined to a local scope, ensuring encapsulation.
2. It becomes more evident which classes share a relationship, enhancing code readability.

Although inner or nested classes provide structural benefits, they’re not as commonly used in Python compared to other OOP languages.

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