List comprehension with condition in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a list of squares of numbers from 1 to 5.

Python

squares = [x[1]2 for x in range(1, 6)]
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 (+) instead of exponentiation.

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

2fill in blank

medium

Complete the code to create a list of even numbers from 1 to 10 using list comprehension with a condition.

Python

evens = [x for x in range(1, 11) if x [1] 2 == 0]
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 modulus (%).

Using floor division (//) instead of modulus.

The % operator gives the remainder of division. If x % 2 == 0, x is even.

3fill in blank

hard

Fix the error in the list comprehension to get numbers greater than 5 from the list.

Python

numbers = [1, 3, 6, 8, 2]
greater_than_five = [n for n in numbers if n [1] 5]
print(greater_than_five)

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

A>

B<=

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than (<) instead of greater than (>).

Using equality (==) instead of comparison.

To get numbers greater than 5, use the greater than operator >.

4fill in blank

hard

Fill both blanks to create a list of squares of odd numbers from 1 to 10.

Python

odd_squares = [x[1]2 for x in range(1, 11) if x [2] 2 != 0]
print(odd_squares)

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

A**

B+

C%

D//

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition (+) instead of exponentiation.

Using floor division (//) instead of modulus.

Use ** to square the number and % to check if the number is odd by checking remainder not equal to zero.

5fill in blank

hard

Fill all three blanks to create a list of uppercase words that have length greater than 3.

Python

words = ['apple', 'bat', 'carrot', 'dog']
result = [[1].upper() for [2] in words if len([3]) > 3]
print(result)

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

Aword

Dwords

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Applying .upper() to the list instead of the word.

Use the variable word consistently to refer to each item in the list. Apply .upper() to convert to uppercase and check length with len(word) > 3.

Practice

1. What does the following list comprehension do?
[x for x in range(5) if x % 2 == 0]

easy

A. Creates a list of odd numbers from 0 to 4

B. Creates a list of even numbers from 0 to 4

C. Creates a list of numbers from 1 to 5

D. Creates a list of numbers divisible by 3

Solution

1. Step 1: Understand the range and condition

   The range(5) generates numbers 0, 1, 2, 3, 4. The condition x % 2 == 0 selects numbers divisible by 2 (even numbers).

2. Step 2: Apply the condition to each number

   From 0 to 4, the even numbers are 0, 2, and 4. These are included in the new list.

3. Final Answer:

   [0, 2, 4] -> Option B

4. Quick Check:

   Even numbers from 0 to 4 = [0, 2, 4] [OK]

Hint: Look for the condition after 'if' to filter items [OK]

Common Mistakes:

• Confusing even and odd numbers
• Ignoring the condition and taking all numbers
• Misunderstanding the range function

2. Which of the following is the correct syntax for a list comprehension that selects numbers greater than 10 from list nums?

easy

A. [x for x > 10 in nums]

B. [x if x > 10 for x in nums]

C. [if x > 10 for x in nums]

D. [x for x in nums if x > 10]

Solution

1. Step 1: Recall list comprehension syntax

   The correct syntax is [expression for item in iterable if condition]. Here, expression and item are both x, iterable is nums, and condition is x > 10.

2. Step 2: Check each option

   [x for x in nums if x > 10] matches the correct syntax. The other options have misplaced or missing parts.

3. Final Answer:

   [x for x in nums if x > 10] -> Option D

4. Quick Check:

   Correct list comprehension syntax = [x for x in nums if x > 10] [OK]

Hint: Remember: for comes before if in list comprehension [OK]

Common Mistakes:

• Placing 'if' before 'for'
• Omitting 'for' keyword
• Using incorrect order of clauses

3. What is the output of this code?

nums = [3, 7, 12, 5, 20]
result = [n*2 for n in nums if n > 6]
print(result)

medium

A. [14, 24, 40]

B. [3, 7, 12, 5, 20]

C. [6, 14, 24, 10, 40]

D. [12, 24, 40]

Solution

1. Step 1: Identify numbers greater than 6

   From the list, numbers greater than 6 are 7, 12, and 20.

2. Step 2: Multiply each selected number by 2

   7*2=14, 12*2=24, 20*2=40. These form the new list.

3. Final Answer:

   [14, 24, 40] -> Option A

4. Quick Check:

   Filter >6 and double = [14, 24, 40] [OK]

Hint: Apply condition first, then transform each item [OK]

Common Mistakes:

• Multiplying all numbers, ignoring condition
• Including numbers less than or equal to 6
• Confusing multiplication with addition

4. Find the error in this list comprehension:

values = [1, 2, 3, 4]
new_values = [x for x in values if x > 2 else 0]

medium

A. SyntaxError due to incorrect use of else in list comprehension

B. No error, code runs fine

C. TypeError because of wrong condition

D. NameError because x is undefined

Solution

1. Step 1: Understand list comprehension with condition

   In list comprehension, 'if' can be used to filter items, but 'else' must be part of a conditional expression, not after 'if' alone.

2. Step 2: Identify the syntax error

   The code uses 'if x > 2 else 0' incorrectly. The correct way is to use a conditional expression inside the expression part, like [x if x > 2 else 0 for x in values].

3. Final Answer:

   SyntaxError due to incorrect use of else in list comprehension -> Option A

4. Quick Check:

   Else must be inside expression, not after if clause [OK]

Hint: Use if-else inside expression, not after if clause [OK]

Common Mistakes:

• Placing else after if in list comprehension filter
• Confusing filter condition with conditional expression
• Ignoring Python syntax rules for comprehensions

5. You have a list of strings: words = ['apple', '', 'banana', 'cherry', '', 'date']. Which list comprehension creates a new list with only non-empty strings in uppercase?

hard

A. [w for w in words if w.upper()]

B. [w.upper() if w else w for w in words]

C. [w.upper() for w in words if w]

D. [w.upper() for w in words if w == '']

Solution

1. Step 1: Understand filtering non-empty strings

   In Python, empty strings are false in boolean context. Using if w filters out empty strings.

2. Step 2: Convert filtered strings to uppercase

   For each non-empty string w, w.upper() converts it to uppercase.

3. Final Answer:

   [w.upper() for w in words if w] -> Option C

4. Quick Check:

   Filter non-empty and uppercase = [w.upper() for w in words if w] [OK]

Hint: Use 'if w' to filter non-empty strings in list comprehension [OK]

Common Mistakes:

• Filtering empty strings incorrectly
• Using if-else incorrectly inside comprehension
• Not converting strings to uppercase