Nested for loop execution in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested loops with range

What is the output of this Python code?

Python

result = []
for i in range(2):
    for j in range(3):
        result.append((i, j))
print(result)

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

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

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

D [(0, 0), (1, 1), (2, 2), (3, 3)]

💡 Hint

Think about how the inner loop runs completely for each step of the outer loop.

The outer loop runs for i=0 and i=1. For each i, the inner loop runs j=0,1,2. So pairs are (0,0),(0,1),(0,2),(1,0),(1,1),(1,2).

❓ Predict Output

intermediate

Sum of products in nested loops

What is the value of variable total after running this code?

Python

total = 0
for x in range(1, 4):
    for y in range(1, 3):
        total += x * y
print(total)

A 18

B 20

C 24

D 12

💡 Hint

Calculate the sum of x*y for x=1 to 3 and y=1 to 2.

The pairs are (1,1),(1,2),(2,1),(2,2),(3,1),(3,2). Their products sum to 1+2+2+4+3+6=18.

🔧 Debug

advanced

Identify the error in nested loops

What error does this code raise when run?

Python

for i in range(3):
    for j in range(2):
        print(i, j)

A SyntaxError

B TypeError

C IndentationError

D No error, prints pairs

💡 Hint

Check the syntax of the for loops carefully.

The inner for loop is missing a colon at the end, causing a SyntaxError.

❓ Predict Output

advanced

Output of nested loops with break

What is the output of this code?

Python

result = []
for a in range(3):
    for b in range(3):
        if b == 1:
            break
        result.append((a, b))
print(result)

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

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

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

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

💡 Hint

The break stops the inner loop when b equals 1.

For each a, b starts at 0. When b == 1, the inner loop breaks, so only (a,0) is appended for each a.

🧠 Conceptual

expert

Number of iterations in nested loops

How many times will the innermost statement print(i, j, k) execute in this code?

Python

for i in range(2):
    for j in range(3):
        for k in range(4):
            print(i, j, k)

A 6

B 9

C 12

D 24

💡 Hint

Multiply the lengths of all ranges to find total iterations.

The loops run 2 * 3 * 4 = 24 times, so print runs 24 times.