Basic list comprehension syntax in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of simple list comprehension

What is the output of this Python code?

Python

result = [x * 2 for x in range(4)]
print(result)

A [0, 2, 4, 6]

B [1, 2, 3, 4]

C [2, 4, 6, 8]

D [0, 1, 2, 3]

💡 Hint

Think about what range(4) produces and how each element is multiplied by 2.

range(4) produces 0,1,2,3. Multiplying each by 2 gives 0,2,4,6.

❓ Predict Output

intermediate

List comprehension with condition

What is the output of this code?

Python

result = [x for x in range(6) if x % 2 == 0]
print(result)

A [1, 3, 5]

B [0, 1, 2, 3, 4, 5]

C [0, 2, 4]

D [2, 4, 6]

💡 Hint

The condition filters numbers divisible by 2.

The list comprehension includes only even numbers from 0 to 5, which are 0, 2, and 4.

❓ Predict Output

advanced

Nested list comprehension output

What is the output of this nested list comprehension?

Python

result = [(x, y) for x in range(2) for y in range(3)]
print(result)

A [(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2)]

B [(0, 0), (1, 0), (0, 1), (1, 1), (0, 2), (1, 2)]

C [(0, 0), (1, 0), (2, 0), (0, 1), (1, 1), (2, 1)]

D [(0, 0), (0, 1), (1, 0), (1, 1), (2, 0), (2, 1)]

💡 Hint

The first loop is x, the second is y, so y changes faster.

The comprehension pairs each x with every y in order, producing all combinations with x from 0 to 1 and y from 0 to 2.

❓ Predict Output

advanced

List comprehension with else clause (ternary)

What is the output of this code?

Python

result = [x if x % 2 == 0 else -x for x in range(5)]
print(result)

A [0, 1, 2, 3, 4]

B [0, -1, 2, -3, 4]

C [-0, 1, -2, 3, -4]

D [0, -1, -2, -3, -4]

💡 Hint

If x is even, keep it; if odd, make it negative.

For each number from 0 to 4, even numbers stay the same, odd numbers become negative.

🧠 Conceptual

expert

Understanding list comprehension order

Which option correctly describes the order in which elements are generated in this list comprehension?

result = [(x, y) for x in range(3) for y in range(2)]

A Only pairs where x equals y are included.

B For each y, all x values are paired before moving to the next y.

C Pairs are generated randomly without order.

D For each x, all y values are paired before moving to the next x.

💡 Hint

Think about how nested loops work in Python.

The comprehension is like nested loops: for each x, it loops through all y values, pairing them in order.