While–else behavior in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Done" after the while loop finishes normally.

Python

count = 0
while count < 3:
    print(count)
    count += 1
else:
    print([1])

Drag options to blanks, or click blank then click option'

Acount

B"Done"

CDone

D"count"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string in print.

Trying to print the variable count instead of the message.

The else block runs after the while loop finishes normally. Printing the string "Done" shows this.

2fill in blank

medium

Complete the code to break the loop when count reaches 2.

Python

count = 0
while count < 5:
    if count == [1]:
        break
    print(count)
    count += 1
else:
    print("Finished")

Drag options to blanks, or click blank then click option'

A2

B4

C5

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number outside the loop range.

Not breaking the loop at the correct count.

The loop breaks when count equals 2, so the else block will not run.

3fill in blank

hard

Fix the error in the else block to print "Loop ended" only if no break occurs.

Python

i = 0
while i < 4:
    if i == 5:
        break
    print(i)
    i += 1
else:
    print([1])

Drag options to blanks, or click blank then click option'

A"Loop ended"

BLoop ended

Ci

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Printing a variable instead of a string.

Missing quotes causing a NameError.

The else block prints the string "Loop ended" only if the loop finishes without break. The string must be in quotes.

4fill in blank

hard

Fill both blanks to create a dictionary of squares for numbers less than 5, but only if the number is even.

Python

squares = {x: x[1]2 for x in range(5) if x [2] 2 == 0}

Drag options to blanks, or click blank then click option'

A**

B%

C==

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of ** for squares.

Using == instead of % for checking evenness.

The expression x**2 calculates the square. The condition x % 2 == 0 checks if x is even.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase keys and values greater than 1.

Python

result = { [1]: [2] for k, v in data.items() if v [3] 1 }

Drag options to blanks, or click blank then click option'

Ak.upper()

Bv

C>

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using k instead of k.upper() for keys.

Using < instead of > in the condition.

The key is converted to uppercase with k.upper(). The value v is used. The condition v > 1 filters values greater than 1.

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