Assert statement usage in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of assert with a failing condition

What will be the output when running this code?

Python

def check_positive(x):
    assert x > 0, "Value must be positive"
    return x

print(check_positive(-5))

A Value must be positive

B AssertionError: Value must be positive

C -5

D null

💡 Hint

Remember what assert does when the condition is false.

The assert statement checks if the condition is true. If false, it raises an AssertionError with the given message.

❓ Predict Output

intermediate

Assert statement with no message

What is the output of this code snippet?

Python

def test_value(val):
    assert val == 10
    return "Passed"

print(test_value(5))

A 5

B Passed

C AssertionError

D null

💡 Hint

What happens if assert condition is false and no message is given?

Assert raises AssertionError without a message if the condition is false.

❓ Predict Output

advanced

Effect of disabling assert statements

What will be the output of this code when run with python -O (optimize) flag?

Python

def check():
    assert false, "Fail"
    return "Checked"

print(check())

A null

B AssertionError: Fail

C false

D Checked

💡 Hint

The -O flag disables assert statements.

When Python runs with -O, assert statements are ignored, so the function returns "Checked".

🧠 Conceptual

advanced

Purpose of assert statements in code

Which of the following best describes the main purpose of assert statements in Python?

A To check conditions during development and catch bugs early

B To improve program performance by skipping checks

C To replace if-else statements for decision making

D To handle runtime errors gracefully

💡 Hint

Think about when and why developers use assert.

Assert statements are used to verify assumptions during development and testing, helping catch bugs early.

❓ Predict Output

expert

Output with assert inside a loop and else clause

What is the output of this code?

Python

for i in range(3):
    assert i < 2, f"Index {i} too high"
else:
    print("Loop completed")

A AssertionError: Index 2 too high

B Loop completed

C 0\n1\n2

D null

💡 Hint

Check when the assert fails and if the else block runs.

The assert fails when i is 2, raising AssertionError before the else block can run.