How variable type changes at runtime in Python - Performance & Efficiency

Time Complexity: How variable type changes at runtime

O(n)

Understanding Time Complexity

We want to see how the time it takes to run code changes when a variable changes its type during the program.

How does this affect the speed as the program runs?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

x = 10
x = "hello"
x = [1, 2, 3]
for item in x:
    print(item)

This code changes the variable x from a number to a string, then to a list, and finally loops over the list to print each item.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping over the list x to print each item.
• How many times: Once for each item in the list (3 times here).

How Execution Grows With Input

As the list x gets bigger, the loop runs more times, once per item.

Input Size (n)	Approx. Operations
10	10 print operations
100	100 print operations
1000	1000 print operations

Pattern observation: The time grows directly with the number of items in the list.

Final Time Complexity

Time Complexity: O(n)

This means the time to run the loop grows in a straight line with the number of items in the list.

Common Mistake

[X] Wrong: "Changing the variable type multiple times makes the program slower in a way that depends on the number of changes."

[OK] Correct: Changing the variable type itself is a simple assignment and happens once each time; it does not repeat or grow with input size, so it does not affect the overall time complexity significantly.

Interview Connect

Understanding how variable types can change and how loops behave helps you explain how your code runs as data grows, a key skill in many programming tasks.

Self-Check

"What if the variable x was changed to a dictionary instead of a list? How would the time complexity change when looping over it?"