List comprehension vs loop in Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a list of squares using a loop.

Python

squares = []
for i in range(5):
    squares.append(i[1]2)
print(squares)

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

A-

B*

C+

D**

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication (*) instead of exponentiation (**).

Using addition (+) or subtraction (-) by mistake.

The ** operator is used to raise a number to a power. Here, i**2 means i squared.

2fill in blank

medium

Complete the list comprehension to create a list of squares.

Python

squares = [i[1]2 for i in range(5)]
print(squares)

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

A**

B+

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication (*) instead of exponentiation (**).

Using addition (+) or subtraction (-) by mistake.

In list comprehensions, you can use the same operators as in regular code. Here, i**2 squares each number.

3fill in blank

hard

Fix the error in the loop that tries to create a list of even numbers.

Python

evens = []
for num in range(10):
    if num [1] 2 == 0:
        evens.append(num)
print(evens)

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

A//

B+

C%

D**

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition (+) instead of modulo (%).

Using floor division (//) or exponentiation (**) incorrectly.

The modulo operator % gives the remainder of division. num % 2 == 0 checks if num is even.

4fill in blank

hard

Fill both blanks to create a list of even squares using list comprehension.

Python

even_squares = [x[1]2 for x in range(10) if x [2] 2 == 0]
print(even_squares)

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

A**

B%

C==

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition (+) or equality (==) in the wrong place.

Mixing up operators for squaring and checking evenness.

The first blank uses ** to square the number. The second blank uses % to check if the number is even.

5fill in blank

hard

Fill all three blanks to create a dictionary of numbers and their squares for odd numbers only.

Python

odd_squares = [1]: [1] for [2] in range(10) if [3] % 2 != 0}
print(odd_squares)

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

Anum

Bnum**2

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not squaring the number for the value.

The dictionary comprehension uses num as the key and num**2 as the value. The variable num iterates over the range.

Practice

1. What is the main advantage of using list comprehension over a traditional for loop in Python?

easy

A. It runs slower than a loop

B. It creates lists in fewer lines and is more readable

C. It cannot be used to create lists

D. It requires more code to write

Solution

1. Step 1: Understand list comprehension purpose

   List comprehension is designed to create lists in a concise and readable way.

2. Step 2: Compare with traditional loops

   Traditional loops require more lines and are less compact than list comprehensions.

3. Final Answer:

   It creates lists in fewer lines and is more readable -> Option B

4. Quick Check:

   List comprehension = concise and readable [OK]

Hint: List comprehension is shorter and clearer than loops [OK]

Common Mistakes:

• Thinking list comprehension is slower
• Believing list comprehension can't create lists
• Confusing loops as always simpler

2. Which of the following is the correct syntax for a list comprehension that creates a list of squares of numbers from 0 to 4?

easy

A. [x**2 for x in range(5)]

B. [for x in range(5) x**2]

C. [x^2 in range(5)]

D. for x in range(5): x**2

Solution

1. Step 1: Recall list comprehension syntax

   The correct syntax is: [expression for variable in iterable].

2. Step 2: Check each option

   [x**2 for x in range(5)] matches the correct syntax. Others have syntax errors or missing parts.

3. Final Answer:

   [x**2 for x in range(5)] -> Option A

4. Quick Check:

   Correct list comprehension syntax = [x**2 for x in range(5)] [OK]

Hint: Remember: [expression for variable in iterable] [OK]

Common Mistakes:

• Placing 'for' after expression
• Using ^ instead of ** for power
• Writing loop without brackets

3. What is the output of the following code?

nums = [1, 2, 3]
squares = []
for n in nums:
    squares.append(n**2)
print(squares)

medium

A. [1, 2, 3]

B. [2, 4, 6]

C. [1, 4, 9]

D. Error

Solution

1. Step 1: Understand the loop operation

   The loop goes through each number in nums and appends its square to squares.

2. Step 2: Calculate squares for each element

   1 squared is 1, 2 squared is 4, 3 squared is 9, so squares = [1, 4, 9].

3. Final Answer:

   [1, 4, 9] -> Option C

4. Quick Check:

   Squares of [1,2,3] = [1,4,9] [OK]

Hint: Loop appends squares, so output is squared list [OK]

Common Mistakes:

• Confusing append with extend
• Expecting original list instead of squares
• Syntax errors in loop

4. Identify the error in this list comprehension:

result = [x*2 for x in range(5)
print(result)

medium

A. print statement is incorrect

B. Using wrong operator * instead of **

C. range(5) should be range[5]

D. Missing closing bracket "]" in list comprehension

Solution

1. Step 1: Check list comprehension syntax

   The list comprehension is missing the closing square bracket "]" at the end.

2. Step 2: Verify other parts

   Operator * is correct for multiplication, range(5) is correct, and print syntax is valid.

3. Final Answer:

   Missing closing bracket "]" in list comprehension -> Option D

4. Quick Check:

   Syntax error due to missing bracket [OK]

Hint: Always close brackets in comprehensions [OK]

Common Mistakes:

• Forgetting closing bracket
• Confusing parentheses and brackets
• Misusing range syntax

5. You want to create a list of even numbers from 0 to 10 using list comprehension. Which code correctly does this?

hard

A. [x for x in range(11) if x % 2 == 0]

B. [x*2 for x in range(5)]

C. [x for x in range(10) if x % 2]

D. [x for x in range(11) if x / 2 == 0]

Solution

1. Step 1: Understand the requirement

   We want even numbers from 0 to 10 inclusive, so numbers divisible by 2.

2. Step 2: Analyze each option

   [x for x in range(11) if x % 2 == 0] uses correct range and condition (x % 2 == 0). [x*2 for x in range(5)] doubles numbers 0-4, giving [0,2,4,6,8]. [x for x in range(10) if x % 2] filters odd numbers (x % 2 is true for odd). [x for x in range(11) if x / 2 == 0] uses division instead of modulo, which is incorrect.

3. Final Answer:

   [x for x in range(11) if x % 2 == 0] -> Option A

4. Quick Check:

   Filter even numbers with modulo == 0 [OK]

Hint: Use modulo % 2 == 0 to filter even numbers [OK]

Common Mistakes:

• Using multiplication instead of filtering
• Using wrong condition for even check
• Confusing division with modulo