What is inheritance?

Question

IT Interview Practice · Accepted Answer

**Inheritance** lets a class (the *subclass* or *child*) reuse and extend the fields and methods of another class (the *superclass* or *parent*). It models an **is-a** relationship: a `Dog` *is an* `Animal`.

## Reuse and extend

```python
class Animal:
    def __init__(self, name):
        self.name = name
    def eat(self):
        return f"{self.name} is eating"

class Dog(Animal):              # Dog inherits everything from Animal
    def bark(self):            # ...and adds new behavior
        return "Woof!"

d = Dog("Rex")
print(d.eat())                 # "Rex is eating"  → inherited, not rewritten
print(d.bark())                # "Woof!"          → Dog-specific
```

`Dog` got `__init__` and `eat` for free and added `bark`. A subclass can also **override** inherited methods to change behavior.

## Trade-offs

| Benefit | Risk |
|---|---|
| Reuse shared code | Tight coupling to the parent |
| Model real hierarchies | Fragile base class — parent changes break children |
| Polymorphism via a common type | Deep trees become hard to follow |

A common guideline: **favor composition over inheritance** when the relationship is really "has-a," not "is-a."

## Why it matters

Inheritance is the most-misused OOP feature: it's tempting to use it just to share code, which couples unrelated classes.

Used correctly — only for genuine is-a relationships — it gives you reuse plus polymorphism, letting you treat many subtypes uniformly through their common parent.

Benefit	Risk
Reuse shared code	Tight coupling to the parent
Model real hierarchies	Fragile base class — parent changes break children
Polymorphism via a common type	Deep trees become hard to follow

Reuse and extend

Trade-offs

Why it matters

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