Infinite loop prevention in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Detecting infinite loop with a missing update

What will be the output of this code snippet?

Python

count = 0
while count < 3:
    print(count)
    # Missing count update here

A SyntaxError

B

0
1
2

C

0
0
0
... (infinite loop)

D 0

💡 Hint

Check if the loop variable changes inside the loop.

The variable 'count' is never updated inside the loop, so the condition 'count < 3' is always true, causing an infinite loop printing 0 repeatedly.

❓ Predict Output

intermediate

Loop with break to prevent infinite iteration

What is the output of this code?

Python

i = 0
while True:
    print(i)
    i += 1
    if i == 3:
        break

A SyntaxError

B

0
1
2
3

C Infinite loop printing numbers

D

0
1
2

💡 Hint

Look for the break condition inside the loop.

The loop prints 0, 1, 2 and then breaks when i reaches 3, so it stops before printing 3.

❓ Predict Output

advanced

Infinite loop caused by wrong loop condition update

What will be the output of this code?

Python

n = 5
while n > 0:
    print(n)
    n += 1

A

5
6
7
... (infinite loop)

B 0

C

5
4
3
2
1

D SyntaxError

💡 Hint

Check if the loop variable moves towards the exit condition.

The variable 'n' increases each time, so 'n > 0' is always true, causing an infinite loop printing increasing numbers starting from 5.

❓ Predict Output

advanced

Infinite loop due to mutable default argument in recursion

What will happen when this function is called as 'func()'?

Python

def func(lst=None):
    if lst is None:
        lst = []
    lst.append(1)
    print(lst)
    if len(lst) < 3:
        func(lst)
func()

A

[1]
[1, 1]
[1, 1, 1]

B Infinite recursion causing RecursionError

C SyntaxError

D

[1]
[1, 1]
[1, 1, 1, 1]

💡 Hint

Look at how the list grows and when recursion stops.

The function appends 1 to the list and calls itself until the list length reaches 3, then stops, printing the list at each step.

🧠 Conceptual

expert

Best practice to prevent infinite loops in complex code

Which option is the best practice to prevent infinite loops in complex programs?

A Use only for-loops instead of while-loops

B Always include a maximum iteration count or timeout condition in loops

C Avoid using break statements inside loops

D Never update loop variables inside the loop

💡 Hint

Think about how to stop loops that might run too long.

Including a maximum iteration count or timeout ensures loops stop even if the main exit condition fails, preventing infinite loops in complex or unexpected cases.