While–else behavior in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the else block do in a while–else statement?

The else block runs only if the while loop finishes normally without encountering a break statement.

beginner

When is the else block skipped in a while–else loop?

The else block is skipped if the while loop exits early due to a break statement.

beginner

Consider this code:

i = 0
while i < 3:
    print(i)
    i += 1
else:
    print('Done')

What will be printed?

The output will be:
0
1
2
Done
The else runs because the loop finished normally.

beginner

What happens if a break is used inside a while loop with an else?

If break runs, the loop stops immediately and the else block does not run.

intermediate

Why might you use a while–else instead of just a while loop?

You use while–else to run special code only if the loop did not stop early, like confirming a search found nothing.

What triggers the else block in a while–else loop?

A The loop contains a break

B The loop runs at least once

C The loop finishes without a break

D The loop condition is false initially

The else block runs only if the loop finishes normally without a break.

If a while loop never runs because the condition is false at start, does the else block run?

A Yes, because the loop did not break

B No, never

C Yes, always

D Only if there is a break

The else block runs if the loop condition is false initially and the loop body never executes.

What happens if a break is inside the while loop?

A The <code>else</code> block runs after break

B The <code>else</code> block is skipped

C The loop restarts

D The program crashes

A break stops the loop early and skips the else block.

Which of these is a good use of while–else?

A To run code only if the loop breaks

B To run code before the loop starts

C To run code inside the loop

D To run code after a loop that found no matching item

while–else is useful to run code if the loop completes without finding something.

What will this code print?

i = 0
while i < 5:
    if i == 3:
        break
    print(i)
    i += 1
else:
    print('Finished')

A 0 1 2

B 0 1 2 Finished

C Finished

D 0 1 2 3 4 Finished

The loop breaks at i == 3, so else does not run. It prints 0,1,2 only.

Explain how the else block works with a while loop in Python.

Think about when the loop ends normally versus early.

Describe a real-life example where a while–else loop would be helpful.

Imagine looking for your keys and what you do if you find or don't find them.

Practice

1.

What happens to the else block in a while loop if the loop ends normally (without a break)?

easy

A. The else block runs before the loop starts.

B. The else block never runs.

C. The else block runs after the loop finishes all iterations.

D. The else block runs only if the loop has a break.

Solution

1. Step 1: Understand the while-else structure

   The else block after a while loop runs only if the loop finishes all iterations without encountering a break.

2. Step 2: Analyze loop ending conditions

   If the loop ends normally (condition becomes false), the else block executes. If a break occurs, it skips the else.

3. Final Answer:

   The else block runs after the loop finishes all iterations. -> Option C

4. Quick Check:

   while-else else runs if no break [OK]

Hint: Else runs only if while loop ends without break [OK]

Common Mistakes:

• Thinking else runs always after while
• Believing else runs only if break occurs
• Confusing else with finally block

2.

Which of the following is the correct syntax for a while loop with an else block in Python?

?

easy

A. while condition:
# code
else
# code

B. while condition:
else:
# code
# code

C. while condition:
# code
else:
# code

D. while condition:
# code
else:
# code

Solution

1. Step 1: Recall Python while-else syntax

   The else block must be aligned with the while, not indented inside it.

2. Step 2: Check each option's indentation and keywords

   while condition: # code else: # code correctly places else: aligned with while and indents code blocks properly.

3. Final Answer:

   while condition: # code else: # code -> Option D

4. Quick Check:

   Else aligned with while, colon included [OK]

Hint: Else must align with while, not inside loop body [OK]

Common Mistakes:

• Indenting else inside while block
• Missing colon after else
• Placing else before while

3.

What is the output of this code?

i = 0
while i < 3:
    print(i)
    i += 1
else:
    print('Done')

medium

A. 0
1
2

B. 0
1
2
Done

C. Done

D. 0
1
2
3
Done

Solution

1. Step 1: Trace the while loop iterations

   Variable i starts at 0 and increments by 1 each loop until i < 3 is false. It prints 0, 1, 2.

2. Step 2: Check else block execution

   Since the loop ends normally (i becomes 3, condition false), the else block runs and prints 'Done'.

3. Final Answer:

   0 1 2 Done -> Option B

4. Quick Check:

   Loop prints 0-2, else prints Done [OK]

Hint: Else runs after loop if no break, prints 'Done' [OK]

Common Mistakes:

• Ignoring else block output
• Expecting 3 to print inside loop
• Thinking else runs only on break

4.

Find the error in this code snippet:

i = 0
while i < 5:
    if i == 3:
        break
    print(i)
    i += 1
else:
print('Finished')

medium

A. The else block is not indented properly.

B. The break statement is outside the loop.

C. The while condition is invalid.

D. The print statement inside the loop is missing parentheses.

Solution

1. Step 1: Check indentation of else block

   The else block must be aligned with the while statement, but here it is not indented properly.

2. Step 2: Verify other parts

   Break is inside the loop, while condition is valid, and print uses parentheses correctly.

3. Final Answer:

   The else block is not indented properly. -> Option A

4. Quick Check:

   Else must align with while, indentation error [OK]

Hint: Else must align with while, check indentation [OK]

Common Mistakes:

• Misplacing else inside loop body
• Confusing break placement
• Ignoring indentation errors

5.

Consider this code:

n = 5
while n > 0:
    if n == 3:
        break
    print(n)
    n -= 1
else:
    print('Loop completed')

What will be the output and why?

hard

A. 5
4
Because break stops loop, else does not run.

B. 5
4
3
Loop completed
Because else always runs.

C. 5
4
3
Because break is inside if, else runs anyway.

D. Loop completed
Because else runs before loop.

Solution

1. Step 1: Trace loop iterations and break

   n starts at 5, prints 5 and 4. When n == 3, break stops the loop immediately.

2. Step 2: Understand else block behavior

   Because the loop was stopped by break, the else block does not run, so 'Loop completed' is not printed.

3. Final Answer:

   5 4 Because break stops loop, else does not run. -> Option A

4. Quick Check:

   Break skips else, so only 5 and 4 print [OK]

Hint: Break skips else; else runs only if no break [OK]

Common Mistakes:

• Assuming else runs even after break
• Printing 3 inside loop
• Thinking else runs before loop