Python Inheritance

Python Inheritance: Reusing and Extending Classes with super()

Python inheritance lets a child class (subclass) reuse attributes and methods from a parent class (base class). You write shared logic once in the parent and customize only the differences in each child.

Pass the parent class name in parentheses after the child class name (class AdminUser(User):). When both classes define the same method name, the child's version overrides the parent's.

Overriding Methods and Calling super()

Always use super().__init__(...) inside a child's __init__ so the parent initializes its attributes cleanly without hardcoding the parent class name.

class Notification:
    def __init__(self, recipient: str) -> None:
        self.recipient = recipient

    def send(self, message: str) -> str:
        return f"Sending to {self.recipient}: {message}"

class EmailNotification(Notification):
    def __init__(self, recipient: str, subject: str) -> None:
        super().__init__(recipient)
        self.subject = subject

    def send(self, message: str) -> str:
        base = super().send(message)
        return f"[{self.subject}] {base}"

note = EmailNotification("[email protected]", "Deploy Ready")
print(note.send("Build v2.4 passed"))

Checking Relationships Safely

Use isinstance(note, Notification) (True) to verify compatibility with a base class, or issubclass(EmailNotification, Notification) to inspect class definitions.

Common Mistakes to Avoid

• Skipping super().__init__() when overriding __init__: Parent attributes never get created, leading to AttributeError later.
• Deep inheritance hierarchies: Three or more layers of subclasses make code fragile; prefer composition (storing a helper object as an attribute) when sharing unrelated features.
• Calling ParentClass.init(self) directly: Hardcoding the parent breaks cooperative multiple inheritance (MRO); super() handles it automatically.

Frequently Asked Questions

Does Python support multiple inheritance?

Yes. A class can inherit from multiple parents (class Child(MixInA, BaseB):), and Python resolves method lookup using the C3 Method Resolution Order (Child.__mro__).

What is an abstract base class (abc.ABC)?

An abstract base class defines @abstractmethod signatures that subclasses must implement before they can be instantiated.

Should I use inheritance or composition?

Use inheritance for strict "is-a" relationships (AdminUser is a User). Use composition ("has-a") when an object simply uses another service or component.