Purpose of constructors in Python - Time & Space Complexity

Time Complexity: Purpose of constructors

O(n)

Understanding Time Complexity

We want to understand how the time it takes to create objects grows as we create more of them.

How does the constructor's work change when we make many objects?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class Car:
    def __init__(self, make, model):
        self.make = make
        self.model = model

cars = []
n = 10
for i in range(n):
    cars.append(Car('Toyota', 'Corolla'))

This code creates a list of n car objects, each initialized with the same make and model.

Identify Repeating Operations

• Primary operation: Calling the constructor Car() inside the loop.
• How many times: Exactly n times, once for each object created.

How Execution Grows With Input

Each new object requires the constructor to run once, so the total work grows directly with the number of objects.

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

Pattern observation: The work grows in a straight line as we add more objects.

Final Time Complexity

Time Complexity: O(n)

This means the time to create all objects grows directly in proportion to how many objects we make.

Common Mistake

[X] Wrong: "Creating many objects is always instant and does not depend on how many we make."

[OK] Correct: Each object needs its constructor to run, so more objects mean more work and more time.

Interview Connect

Understanding how constructors affect time helps you explain how object creation scales in programs, a useful skill when designing efficient code.

Self-Check

"What if the constructor did a complex calculation inside? How would that change the time complexity?"