Why while loop is needed in Python - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a while loop.

Python

count = 1
while [1]:
    print(count)
    count += 1

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

Acount < 1

Bcount = 5

Ccount <= 5

Dcount > 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment '=' instead of comparison '<=' in the condition.

The condition count <= 5 keeps the loop running until count reaches 5.

2fill in blank

medium

Complete the code to keep asking the user for input until they type 'exit'.

Python

user_input = ''
while [1]:
    user_input = input('Type something (or exit): ')
print('Goodbye!')

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

Auser_input > 'exit'

Buser_input != 'exit'

Cuser_input = 'exit'

Duser_input == 'exit'

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment '=' instead of comparison '!=' in the condition.

The loop continues while the input is not 'exit'. When the user types 'exit', the loop stops.

3fill in blank

hard

Fix the error in the code to avoid an infinite loop that prints numbers from 1 to 3.

Python

num = 1
while num <= 3:
    print(num)
    [1]

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

Anum += 1

Bnum -= 1

Cnum = num

Dnum = 3

Attempts:

3 left

💡 Hint

Common Mistakes

Not changing the loop variable, causing an infinite loop.

Incrementing num by 1 ensures the loop will eventually stop when num becomes greater than 3.

4fill in blank

hard

Fill both blanks to create a dictionary of squares for numbers 1 to 5 using a while loop.

Python

squares = {}
i = 1
while [1]:
    squares[i] = i[2]2
    i += 1

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

Ai <= 5

Bi < 5

C**

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '<=' causing missing the last number.

Using '*' instead of '**' for squaring.

The loop runs while i is less than or equal to 5. The exponent operator ** is used to square i.

5fill in blank

hard

Fill all three blanks to create a dictionary of words and their lengths for words longer than 3 letters.

Python

words = ['apple', 'bat', 'carrot', 'dog']
lengths = { [1]: [2] for word in words if len(word) [3] 3 }

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

Aword

Blen(word)

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causing wrong filtering.

Swapping keys and values.

The dictionary uses the word as the key and its length as the value. The condition filters words longer than 3 letters using '>'.

Practice

1. Why do we use a while loop in Python instead of a for loop?

easy

A. Because for loops cannot repeat code.

B. Because we don't always know how many times the loop should run before starting.

C. Because while loops are faster than for loops.

D. Because while loops do not need a condition.

Solution

1. Step 1: Understand the difference between while and for loops

   for loops run a fixed number of times, while while loops run as long as a condition is true.

2. Step 2: Identify when while loops are needed

   while loops are useful when the number of repetitions is unknown before starting.

3. Final Answer:

   Because we don't always know how many times the loop should run before starting. -> Option B

4. Quick Check:

   Unknown repetitions = use while loop [OK]

Hint: Use while when repeat count is unknown before start [OK]

Common Mistakes:

• Thinking for loops can handle unknown repetitions
• Believing while loops don't need conditions
• Confusing speed differences between loops

2. Which of the following is the correct syntax to start a while loop in Python?

easy

A. while x > 0: print(x)

B. while x > 0 print(x):

C. while (x > 0) print x

D. while x > 0 { print(x) }

Solution

1. Step 1: Recall Python's while loop syntax

   Python requires a colon (:) after the condition and indentation for the loop body.

2. Step 2: Check each option

   while x > 0: print(x) uses colon and correct indentation style (single line allowed). Others have syntax errors.

3. Final Answer:

   while x > 0: print(x) -> Option A

4. Quick Check:

   Colon after condition = correct syntax [OK]

Hint: Remember colon (:) after condition in while loops [OK]

Common Mistakes:

• Missing colon after condition
• Using braces {} like other languages
• Incorrect print statement syntax

3. What will be the output of this code?

count = 3
while count > 0:
    print(count)
    count -= 1
print('Done')

medium

A. Done

B. 3 2 1 0 Done

C. 3 2 1 Done

D. 3 2 1

Solution

1. Step 1: Trace the loop iterations

   count starts at 3, prints 3, then decreases to 2, prints 2, then 1, prints 1, then count becomes 0 and loop stops.

2. Step 2: Check what prints after loop

   After loop ends, 'Done' is printed.

3. Final Answer:

   3 2 1 Done -> Option C

4. Quick Check:

   Loop prints 3 to 1, then 'Done' [OK]

Hint: Count down loop prints values until condition false [OK]

Common Mistakes:

• Expecting 0 to print inside loop
• Missing 'Done' print after loop
• Confusing loop stop condition

4. Find the error in this code snippet:

i = 1
while i < 5:
print(i)
    i += 1

medium

A. Indentation error inside the loop

B. Missing colon after while condition

C. Variable i is not initialized

D. Infinite loop because i never changes

Solution

1. Step 1: Check indentation of loop body

   Python requires the code inside the while loop to be indented equally. Here, print(i) is not indented properly.

2. Step 2: Verify other parts

   Colon is present, variable i is initialized, and i increments, so no infinite loop.

3. Final Answer:

   Indentation error inside the loop -> Option A

4. Quick Check:

   Loop body must be indented [OK]

Hint: Indent all loop lines equally to avoid errors [OK]

Common Mistakes:

• Not indenting loop body
• Forgetting colon after while
• Assuming variable needs declaration

5. You want to keep asking a user for a password until they enter the correct one. Which code snippet correctly uses a while loop for this?

hard

A. password = input('Enter password: ')
while password == 'secret':
print('Access granted')

B. while true:\n password = input('Enter password: ')
if password == 'secret':\n break
print('Access granted')

C. for password in ['secret']:\n input('Enter password: ')
print('Access granted')

D. password = ''\nwhile password != 'secret':\n password = input('Enter password: ')
print('Access granted')

Solution

1. Step 1: Understand the goal

   We want to keep asking until the user types 'secret'. This requires input inside the loop and proper exit condition.

2. Step 2: Analyze each option

   password = ''\nwhile password != 'secret':\n password = input('Enter password: ') print('Access granted') initializes empty password, checks condition, inputs inside loop, updates, and exits when equal to 'secret'.
   while true:\n password = input('Enter password: ') if password == 'secret':\n break print('Access granted') uses 'true' which is undefined in Python (must be 'True'), causing NameError.
   for password in ['secret']:\n input('Enter password: ') print('Access granted') uses for loop incorrectly, runs fixed once without checking input.
   password = input('Enter password: ') while password == 'secret': print('Access granted') inputs once then loops only if correct, fails to re-ask on wrong.

3. Final Answer:

   password = ''\nwhile password != 'secret':\n password = input('Enter password: ') print('Access granted') -> Option D

4. Quick Check:

   While != condition + input inside = repeat until match [OK]

Hint: While != target: input() inside loop [OK]

Common Mistakes:

• Using 'true' instead of 'True'
• Using for loop for unknown repeats
• Wrong condition (== instead of !=)