Python Nested Class: A Comprehensive Guide
Published: 2023-05-25 05:54:17

Common Use Cases for Python Nested Classes*
In Python, a nested class is a class that is defined inside another class. The outer class is called the enclosing class, and the inner class is called the nested class. Nested classes are a powerful feature of Python that allow for more flexible and organized code.

The main advantage of using nested classes is that they can access the enclosing class's attributes and methods. This allows for a more modular design, where related classes can be grouped together in a single file and share common functionality.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/3drydu9zv155gmu9rcgp.png)

Additionally, nested classes can be used to create objects that are closely related to the enclosing class. This can be useful in situations where you need to create multiple instances of a particular object, each with its own set of attributes and behavior.

In this comprehensive guide, we will explore the different types of nested classes in Python, their syntax, and practical examples of how to use them effectively.

## Syntax and Declaration of Python Nested Class
In Python, a nested class is a class defined inside another class. This allows the outer class to access the inner class, and vice versa. To declare a nested class, you simply define it inside the outer class. Here's an example:

class OuterClass:
    class InnerClass:
        def __init__(self):
            print("Hello from InnerClass")
  
    def __init__(self):
        print("Hello from OuterClass")
        self.inner = OuterClass.InnerClass()

In this example, the OuterClass has an inner class called InnerClass. The OuterClass constructor creates an instance of InnerClass. To access the inner class from outside the outer class, you can use the dot notation: OuterClass.InnerClass().

### Accessing a Nested Class
To use a nested class, we need to access it via the outer class. The syntax for accessing a nested class is different from a regular class. We need to use the dot notation to access the nested class. For example, if we have a class named "Outer" that contains a nested class named "Inner," we can access the Inner class using the following syntax:

outer_instance = Outer()
inner_instance = outer_instance.Inner()

In this example, we first create an instance of the Outer class and then use that instance to create an instance of the Inner class. We can also create an instance of the Inner class without creating an instance of the Outer class, but that is not a common practice. Once we have an instance of the Inner class, we can use it just like any other class instance.

When it comes to naming conventions for nested classes, the same rules apply as for regular classes. However, it's common practice to use an underscore followed by the name of the outer class before the name of the nested class, to indicate that the nested class is part of the outer class. For example, if we have a class called OuterClass, and we want to define a nested class that represents a point in 2D space, we might call it OuterClass_Point.

## Scope of Python Nested Classes
Nested classes are defined inside another class and have access to all the attributes and methods of the outer class. However, the outer class cannot access the attributes and methods of the nested class. Nested classes are used to group related classes and avoid naming conflicts. The scope of a nested class is limited to the outer class, and it cannot be accessed outside the outer class unless it is explicitly imported. Nested classes can be used to implement encapsulation and improve code readability by grouping related classes together.

### Visibility of Nested Classes

Nested classes in Python can be defined with different levels of visibility. By default, a nested class is considered private, which means that it can only be accessed within the scope of its enclosing class. However, there are ways to make a nested class accessible from outside its enclosing class. One way is to use the public access modifier by prefixing the class definition with the keyword public. Another way is to use the protected access modifier by prefixing the class definition with the keyword protected. These modifiers determine the level of visibility of the nested class and affect how it can be accessed from outside its enclosing class.

### Accessing variables from outer class

Nested classes in Python can have access to the variables of the outer class. To access these variables, the keyword self is used in the nested class definition. The self keyword acts as a reference to the outer class, allowing the nested class to access its variables. For example:

class OuterClass:
    def __init__(self):
        self.outer_variable = "I am an outer variable"
      
    class NestedClass:
        def nested_method(self):
            print(OuterClass().outer_variable)

In this case, NestedClass has access to OuterClass's outer_variable by creating an instance of the OuterClass and using self to access the variable. The nested method nested_method can then use print to display the value of outer_variable.

## Inheritance and Polymorphism of Python Nested Class
In Python, it is possible to create a new class within another class, which is known as a nested class. When a nested class is created, it can be used within the outer class just like any other attribute. One of the most useful features of nested classes is inheritance.

When a subclass is created from an outer class, it can also inherit from the nested classes within it. This allows for more modular and organized code, as related classes can be grouped together. To inherit from a nested class, the subclass must refer to the outer class and the nested class using dot notation, like OuterClass.NestedClass.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/4du9ig9qzr2lllqv26tm.png)

Polymorphism is an important concept in object-oriented programming that allows objects of different classes to be treated as if they were the same class. In Python, nested classes also support polymorphism. This means that they can be used in a similar way to regular classes, but within the scope of another class. By defining nested classes within a parent class, we can use them to create different types of objects that share common properties and behaviors. This is particularly useful for organizing and structuring complex systems and applications.

## Real-world examples of Python Nested Class
Nested classes are used in many real-world scenarios, such as:


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/8z4icmz3b88k9pus00qv.png)

- GUI programming: In GUI programming, nested classes are commonly used to define custom widgets and layouts.
- Database programming: Nested classes can be used to define custom database models.
- Game development: Nested classes can be used to define game objects and their behaviors.
- Mathematical modeling: Nested classes can be used to define mathematical structures such as matrices, vectors, and graphs.
- Web development: Nested classes can be used to define custom data structures and algorithms for web applications.

The possibilities are endless, and nested classes can be used wherever a complex data structure needs to be defined.

Nested class has the ability to create a more organized and clearer structure for your code, making your code more modular and more easily maintainable. Additionally, nested classes can help encapsulate functionality and reduce namespace collisions, which can be a common issue in larger codebases, making it easier to manage and modify in the future.

## Comparison with other programming languages
Python is not the only programming language that supports nested classes. Other languages like Java and C also allow the creation of nested classes. However, the implementation of nested classes in Python is much simpler and more flexible than in these languages.

In Java and C, nested classes are used mainly for organizational purposes and are tightly coupled with their outer class. On the other hand, in Python, nested classes are first-class citizens and can be used independently. Additionally, Python's nested classes provide a convenient way to encapsulate related functionality within a class and improve code organization.

## Best Practices for Python Nested Class
Python's nested classes can be a powerful tool when used correctly. Here are some guidelines to keep in mind when using nested classes:

1. Use nested classes when a class is logically related to another class and will not be used elsewhere in the code.
2. Keep nested classes small and focused on a single responsibility.
3. Use private nested classes for implementation details that should not be accessed directly by the user.
4. Avoid using nested classes for complex inheritance hierarchies or deeply nested structures, as this can make the code difficult to read and maintain.
5. When in doubt, favor using separate classes rather than nesting them.

## Recap on Python Nested Class
To summarize, nested classes in Python are classes defined inside another class. They can be used to logically group related functionalities and increase the readability of the code. We can access the nested class by using the parent class as a namespace. A nested class can also access the attributes and methods of its parent class. 

There are three types of nested classes in Python, namely, inner, local, and static nested classes.

Inner nested classes can access the instance variables of the parent class, local nested classes cannot access instance variables, and static nested classes are independent of the parent class. 

Nested classes can be used to implement encapsulation, abstraction, and information hiding. The use of nested classes in Python has gained popularity over the years, and it is expected to continue to grow as developers find more use cases for it.

Overall, the possibilities for using nested classes in Python are vast, and we can expect to see more innovative uses as developers continue to explore this concept.

## Read more on Python
- [How Do I Extend Class in Python?](https://www.lightly-dev.com/blog/how-to-extend-class-in-python/)
- [Understanding Python Multiple Inheritance: How It Works](https://www.lightly-dev.com/blog/python-multiple-inheritance/)
- [Best Python Code Generators with AI in 2023](https://www.lightly-dev.com/blog/python-code-generator-ai/)

Read more: https://www.lightly-dev.com/blog/python-nested-class/