Python Block Structure and Indentation - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested if-else with indentation

What is the output of this Python code snippet?

Python

x = 5
if x > 3:
    if x < 10:
        print("A")
    else:
        print("B")
else:
    print("C")

A B

B A

C C

D No output

💡 Hint

Check which conditions are true and how indentation groups the print statements.

The first if (x > 3) is true, then the nested if (x < 10) is also true, so it prints "A".

❓ Predict Output

intermediate

Effect of wrong indentation on loop execution

What will be printed by this code?

Python

for i in range(3):
    print(i)
  print('Done')

A IndentationError

B SyntaxError

C

0
1
2
Done

D

0
1
2

💡 Hint

Look carefully at the indentation of the last print statement.

The last print is indented less than the for loop block but not aligned with it, causing IndentationError.

❓ Predict Output

advanced

Output of function with mixed indentation

What is the output of this code?

Python

def f():
    x = 1
    if x == 1:
        print('Yes')
     print('No')
f()

A IndentationError

B

Yes
No

C Yes

D No

💡 Hint

Check the indentation of the second print inside the function.

The second print is indented with 5 spaces, which is inconsistent and causes IndentationError.

❓ Predict Output

advanced

Output of code with multiple blocks and else

What will this code print?

Python

for i in range(2):
    if i == 0:
        print('Zero')
    else:
        print('Not zero')
    print('Loop done')

A

Zero
Loop done
Not zero

B

Zero
Not zero
Loop done
Loop done

C

Zero
Not zero
Loop done

D

Zero
Loop done
Not zero
Loop done

💡 Hint

Notice the indentation of the last print statement inside the loop.

The last print is inside the loop but outside the if-else, so it runs every iteration after the if-else.

🧠 Conceptual

expert

Identifying the cause of unexpected output due to indentation

Consider this code: x = 10 if x > 5: print('Big') if x > 8: print('Very big') else: print('Small') Why does it print only "Big" and "Very big" and never "Small"?

A Because Python ignores else blocks after nested ifs.

B Because the else belongs to the second if, which is true, so else is skipped.

C Because the else belongs to the first if, and x > 5 is true, so else is skipped.

D Because indentation is wrong and else is outside any if.

💡 Hint

Check which if the else is paired with based on indentation.

The else is aligned with the first if, so it runs only if x > 5 is false. Since x=10 > 5, else is skipped.

Practice

1. What does indentation in Python indicate?

easy

A. Which lines of code belong together in a block

B. The data type of a variable

C. The speed of code execution

D. The name of a function

Solution

1. Step 1: Understand Python's use of indentation

   Python uses indentation to group lines of code that belong to the same block, like inside a function or loop.

2. Step 2: Identify what indentation shows

   Indentation shows which lines are connected logically and executed together.

3. Final Answer:

   Which lines of code belong together in a block -> Option A

4. Quick Check:

   Indentation = Code blocks [OK]

Hint: Indentation groups code lines into blocks [OK]

Common Mistakes:

• Thinking indentation shows variable types
• Confusing indentation with execution speed
• Assuming indentation names functions

2. Which of the following code snippets has correct indentation in Python?

easy

A. def greet():
print('Hello')
print('World')

B. def greet():
print('Hello')
print('World')

C. def greet():
print('Hello')
print('World')

D. def greet():
print('Hello')
print('World')

Solution

1. Step 1: Check indentation inside the function

   All lines inside the function must be indented the same amount to belong to the function block.

2. Step 2: Identify the snippet with consistent indentation

   def greet():
     print('Hello')
     print('World')

   has both print statements indented equally under the function, which is correct.

3. Final Answer:

   def greet():\n print('Hello')\n print('World') -> Option D

4. Quick Check:

   Consistent indentation inside function = Correct [OK]

Hint: Indent all block lines equally under the header [OK]

Common Mistakes:

• Mixing indentation levels inside a block
• Not indenting any lines inside a function
• Indenting only some lines inconsistently

3. What will be the output of this code?

for i in range(2):
    print('Start')
    if i == 0:
        print('First loop')
    print('End')

medium

A. Start\nFirst loop\nEnd\nStart\nEnd

B. Start\nEnd\nStart\nFirst loop\nEnd

C. Start\nFirst loop\nEnd\nStart\nFirst loop\nEnd

D. Start\nEnd\nStart\nEnd

Solution

1. Step 1: Trace the loop iterations

   The loop runs twice: i=0 and i=1.

2. Step 2: Check prints for each iteration

   For i=0: prints 'Start', then 'First loop' (because i==0), then 'End'. For i=1: prints 'Start' and 'End' only.

3. Final Answer:

   Start\nFirst loop\nEnd\nStart\nEnd -> Option A

4. Quick Check:

   Loop with condition prints extra line only once [OK]

Hint: Follow indentation to see which prints run inside conditions [OK]

Common Mistakes:

• Ignoring indentation and printing 'First loop' twice
• Mixing order of printed lines
• Assuming all prints run every iteration

4. Identify the error in this code:

if True:
print('Yes')
    print('Still Yes')

medium

A. SyntaxError because of missing colon

B. IndentationError due to inconsistent indentation

C. No error, code runs fine

D. NameError due to undefined variable

Solution

1. Step 1: Check indentation after if statement

   Lines inside the if block must be indented equally.

2. Step 2: Identify inconsistent indentation

   The first print is not indented, the second print is indented. This causes an IndentationError.

3. Final Answer:

   IndentationError due to inconsistent indentation -> Option B

4. Quick Check:

   Inconsistent indentation = IndentationError [OK]

Hint: All lines in a block must have same indentation [OK]

Common Mistakes:

• Thinking missing colon causes error here
• Assuming code runs without indentation
• Confusing IndentationError with NameError

5. You want to write a function that prints numbers 1 to 3, each followed by 'Done' on a new line. Which code correctly uses indentation to achieve this?

def print_numbers():
    for i in range(1, 4):
        print(i)
    print('Done')

hard

A. def print_numbers():
for i in range(1, 4):
print(i)
print('Done')

B. def print_numbers():
for i in range(1, 4):
print(i)
print('Done')

C. def print_numbers():
for i in range(1, 4):
print(i)
print('Done')

D. def print_numbers():
for i in range(1, 4):
print(i)
print('Done')

Solution

1. Step 1: Understand desired output

   Each number 1 to 3 should print, then 'Done' on a new line after each number.

2. Step 2: Check indentation for print statements

   To print 'Done' after each number, both print(i) and print('Done') must be inside the for loop, indented equally.

3. Step 3: Identify correct option

   def print_numbers():
       for i in range(1, 4):
           print(i)
           print('Done')

   has both prints indented inside the loop, so 'Done' prints after each number.

4. Final Answer:

   def print_numbers():\n for i in range(1, 4):\n print(i)\n print('Done') -> Option C

5. Quick Check:

   Same indentation inside loop = prints per iteration [OK]

Hint: Indent all loop actions equally to repeat each time [OK]

Common Mistakes:

• Indenting 'Done' outside loop causing single print
• Not indenting loop body at all
• Mixing indentation levels inside loop