Polymorphism through inheritance in Python - Time & Space Complexity

Time Complexity: Polymorphism through inheritance

O(n)

Understanding Time Complexity

Let's see how the time taken by a program changes when using polymorphism through inheritance.

We want to know how the program's steps grow as we use more objects with inherited behaviors.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class Animal:
    def speak(self):
        pass

class Dog(Animal):
    def speak(self):
        print("Woof")

class Cat(Animal):
    def speak(self):
        print("Meow")

animals = [Dog(), Cat(), Dog()]
for animal in animals:
    animal.speak()

This code creates a list of animals and calls their speak method, which behaves differently depending on the animal type.

Identify Repeating Operations

• Primary operation: Looping through the list of animals and calling their speak method.
• How many times: Once for each animal in the list.

How Execution Grows With Input

Each animal in the list causes one speak call, so the work grows as the list grows.

Input Size (n)	Approx. Operations
10	10 speak calls
100	100 speak calls
1000	1000 speak calls

Pattern observation: The number of operations grows directly with the number of animals.

Final Time Complexity

Time Complexity: O(n)

This means the time grows in a straight line as you add more animals to the list.

Common Mistake

[X] Wrong: "Polymorphism makes the program slower because it adds extra steps for each method call."

[OK] Correct: The extra steps are very small and do not change how the total time grows with more animals; the main factor is still how many animals you have.

Interview Connect

Understanding how polymorphism affects time helps you explain your code's behavior clearly and shows you know how programs scale with more data.

Self-Check

"What if we added a nested loop inside each speak method? How would the time complexity change?"

Practice

1. What does polymorphism through inheritance allow in Python?

easy

A. One method name to have different behaviors in child classes

B. Multiple inheritance from unrelated classes

C. Using the same variable name in different functions

D. Creating objects without defining classes

Solution

1. Step 1: Understand polymorphism concept

   Polymorphism means one method name can behave differently depending on the class.

2. Step 2: Relate to inheritance

   Child classes override the method to provide their own behavior.

3. Final Answer:

   One method name to have different behaviors in child classes -> Option A

4. Quick Check:

   Polymorphism = One method, many behaviors [OK]

Hint: Polymorphism means same method, different actions [OK]

Common Mistakes:

• Confusing polymorphism with multiple inheritance
• Thinking polymorphism means same variable names
• Believing objects can exist without classes

2. Which of the following is the correct way to override a method in a child class?

easy

A. Call the parent method inside the child method without redefining

B. Use the keyword override before the method

C. Define a method with the same name in the child class

D. Rename the method in the child class

Solution

1. Step 1: Check method overriding syntax

   In Python, overriding means defining a method with the same name in the child class.

2. Step 2: Verify other options

   Python does not use override keyword; renaming is not overriding; calling parent method alone is not overriding.

3. Final Answer:

   Define a method with the same name in the child class -> Option C

4. Quick Check:

   Override = same method name in child [OK]

Hint: Override by redefining method name in child class [OK]

Common Mistakes:

• Using a non-existent override keyword
• Thinking calling parent method equals overriding
• Renaming method instead of overriding

3. What will be the output of this code?

class Animal:
    def sound(self):
        return "Some sound"

class Dog(Animal):
    def sound(self):
        return "Bark"

class Cat(Animal):
    def sound(self):
        return "Meow"

animals = [Dog(), Cat(), Animal()]
for a in animals:
    print(a.sound())

medium

A. Bark\nMeow\nSome sound

B. Some sound\nSome sound\nSome sound

C. Bark\nMeow\nError

D. Error\nError\nError

Solution

1. Step 1: Identify method overriding

   Dog and Cat classes override sound method to return "Bark" and "Meow" respectively.

2. Step 2: Trace the loop output

   Loop calls sound() on Dog(), Cat(), and Animal() objects, printing "Bark", "Meow", and "Some sound".

3. Final Answer:

   Bark Meow Some sound -> Option A

4. Quick Check:

   Overridden methods print their own sounds [OK]

Hint: Child method overrides parent, prints child's return [OK]

Common Mistakes:

• Assuming parent method always runs
• Expecting errors from calling base class method
• Mixing output order

4. Find the error in this code that tries to demonstrate polymorphism:

class Vehicle:
    def move(self):
        print("Moving")

class Car(Vehicle):
    def move(self):
        print("Driving")

class Bike(Vehicle):
    def move(self):
        print("Riding")

vehicles = [Car(), Bike()]
for v in vehicles:
    v.move

medium

A. List should include Vehicle() instance

B. Incorrect class inheritance syntax

C. Using print instead of return in methods

D. Missing parentheses when calling move method

Solution

1. Step 1: Check method calls in loop

   The code uses v.move without parentheses, so method is not called.

2. Step 2: Understand effect of missing parentheses

   Without parentheses, method object is referenced but not executed, so no output occurs.

3. Final Answer:

   Missing parentheses when calling move method -> Option D

4. Quick Check:

   Method call needs () to execute [OK]

Hint: Always add () to call methods [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Thinking print vs return causes error here
• Believing inheritance syntax is wrong

5. You want to add a new class Bird that also uses polymorphism with sound(). Which code correctly extends the existing classes and uses polymorphism?

hard

A. class Bird:
def sound(self):
return "Chirp"

animals.append(Bird())
for a in animals:
print(a.sound())

B. class Bird(Animal):
def sound(self):
return "Chirp"

animals.append(Bird())
for a in animals:
print(a.sound())

C. class Bird(Animal):
def noise(self):
return "Chirp"

animals.append(Bird())
for a in animals:
print(a.sound())

D. class Bird(Animal):
def sound(self):
print("Chirp")

animals.append(Bird())
for a in animals:
print(a.sound())

Solution

1. Step 1: Check inheritance and method name

   Bird must inherit from Animal and override sound() method to maintain polymorphism.

2. Step 2: Verify method behavior and usage

   Method returns string "Chirp" like others; appending Bird() to animals list and calling sound() works correctly.

3. Final Answer:

   Correctly inherits Animal and overrides sound() returning "Chirp" -> Option B

4. Quick Check:

   Polymorphism needs same method name and inheritance [OK]

Hint: Inherit and override same method name with matching signature [OK]

Common Mistakes:

• Not inheriting from Animal class
• Using different method name like noise()
• Printing inside method instead of returning