Python Inner Classes

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Python Inner Classes

An inner class is a class defined inside another class.

It is mainly used when a class is closely related to another class and is not useful on its own.

Inner classes help:

    • Organize related code

    • Improve readability

    • Limit the scope of helper classes

Defining an Inner Class

A class can be declared inside another class just like a method.

Example

Creating a basic inner class:

class Container: def __init__(self): self.title = "Main Container" class Item: def show(self): print("This is an item inside the container") box = Container() print(box.title)

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Accessing an Inner Class from Outside

To use an inner class, you must first create an object of the outer class, then create an object of the inner class using that instance.

Example

Accessing and using an inner class:

class Library: def __init__(self): self.name = "City Library" class Book: def info(self): print("Book belongs to the library") library = Library() book = library.Book() book.info()

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Accessing Outer Class Data from an Inner Class

By default, an inner class does not automatically know about the outer class instance.

To access outer class data, pass the outer object explicitly.

Example

Passing the outer class instance:

class Profile: def __init__(self): self.username = "guest_user" class Settings: def __init__(self, profile): self.profile = profile def display(self): print("Profile username:", self.profile.username) profile = Profile() settings = profile.Settings(profile) settings.display()

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Practical Use Case of Inner Classes

Inner classes are useful for modeling components that belong to a larger object.

Example

Using an inner class to represent a laptop’s battery:

class Laptop: def __init__(self, brand): self.brand = brand self.battery = self.Battery() class Battery: def __init__(self): self.level = 0 def charge(self): self.level = 100 print("Battery fully charged") def drain(self): self.level = 10 print("Battery low") def use(self): if self.battery.level > 20: print(f"Using the {self.brand} laptop") else: print("Please charge the battery first") lap = Laptop("Dell") lap.use() lap.battery.charge() lap.use()

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Using Multiple Inner Classes

An outer class can contain more than one inner class to represent different components.

Example

Multiple inner classes inside one class:

class Smartphone: def __init__(self): self.camera = self.Camera() self.speaker = self.Speaker() class Camera: def capture(self): print("Photo captured") class Speaker: def play_sound(self): print("Playing sound") phone = Smartphone() phone.camera.capture() phone.speaker.play_sound()

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