L2 · Working engineerObject-oriented Python~4 min · 4 tests#72

Inheritance in Python: Animal and Dog

Use Python inheritance so Dog reuses Animal's constructor and methods while adding its own speak(). Learn isinstance and method lookup, tested live.

The problem

Animal(name) stores name and has describe() returning "<name> is an animal".
Dog inherits from Animal (no __init__ of its own) and adds speak() returning "Dog barks".

Examples

Example 1
Input
```
Dog("Rex").speak()
```
Expected output
```
'Dog barks'
```
Example 2
Input
```
Dog("Rex").describe()
```
Expected output
```
'Rex is an animal'
```

+ 2 hidden tests on Submit.

Edge cases to ask about

Inherited init
isinstance with parent class

Hints

0/3

How an interviewer scores this

0/9

1. Understand the problemRestate it, ask about edge cases and input size.
2. Write a brute-force solutionCorrect first, clever later.
3. Get the correct outputautoAll visible examples pass.
4. Analyse time complexityautoCommit to a Big-O in the Complexity Lab.
5. Analyse space complexityautoExtra memory, not the input.
6. Identify the bottleneckautoMeasure your code — where does it bend?
7. OptimiseUsually: a set or dict instead of a scan.
8. Explain why it worksSay it out loud to Solvi.
9. Test the edge casesautoSubmit passes every hidden test.

Python 3.13 · Dog

class Animal:
    def __init__(self, name):
        self.name = name

    def describe(self):
        return f"{self.name} is an animal"


class Dog:
    pass

⌘/Ctrl + Enter runs the examples

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Complexity Lab

What does this cost as n grows?

Interviewers score the analysis as much as the code. Commit to an answer first — then check it, and read why.

Time complexity of the optimal solution

Space complexity (extra memory)

Pick both to reveal the answer.

From brute force to optimal

The progression an interviewer wants to hear, one step at a time.

Approach	Time	Space	Idea
class Dog(Animal)	O(1)	O(1)	Attribute lookup walks the MRO: Dog → Animal → object.

Walkthrough of the optimal approach (try it yourself first)

class Dog(Animal) makes Dog a subclass: it gets __init__ and describe from Animal and adds speak. Python finds attributes by walking the MRO (Dog.__mro__).

Inheritance models an is-a relationship. If you only need to reuse behaviour, composition (question 80) is usually the better choice.

Complexity: O(1) time, O(1) space. Method lookup follows a fixed-length chain of classes.

Reveal the reference solution

class Animal:
    def __init__(self, name):
        self.name = name

    def describe(self):
        return f"{self.name} is an animal"


class Dog(Animal):
    def speak(self):
        return "Dog barks"

Follow-ups interviewers ask

What is the MRO with multiple inheritance?
When is composition better?

Frequently asked interview questions

Core interview concepts, complexities, and follow-ups scored by hiring teams.

What is the time complexity of Inheritance in Python: Animal and Dog?

The optimal solution runs in O(1) time and O(1) auxiliary space. Method lookup follows a fixed-length chain of classes.

What follow-up questions do interviewers ask about Inheritance in Python: Animal and Dog?

What is the MRO with multiple inheritance? When is composition better?