List creation and representation in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of list creation with mixed types

What is the output of this Python code?

Python

my_list = [1, '2', 3.0, True]
print(my_list)

A [1, '2', 3.0, True]

B [1, 2, 3.0, True]

C [1, '2', 3, True]

D [1, '2', 3.0, 1]

💡 Hint

Remember that strings and numbers are different types and are shown with quotes or without.

The list contains an integer 1, a string '2', a float 3.0, and a boolean True. The print shows them exactly as stored.

❓ Predict Output

intermediate

Length of a nested list

What is the value of len(my_list) after running this code?

Python

my_list = [1, [2, 3], 4]
print(len(my_list))

A 4

B 3

C 5

D TypeError

💡 Hint

len() counts the top-level items in the list, not inside nested lists.

The list has three items: 1, [2, 3], and 4. The nested list counts as one item.

❓ Predict Output

advanced

Output of list multiplication with nested lists

What is the output of this code?

Python

lst = [[0]] * 3
lst[0][0] = 5
print(lst)

A [[5], [5], [5]]

B [[0], [0], [0]]

C [[5], [0], [0]]

D TypeError

💡 Hint

Multiplying a list with nested lists copies references, not independent copies.

All three elements point to the same inner list. Changing one changes all.

❓ Predict Output

advanced

Output of list comprehension with condition

What is the output of this code?

Python

result = [x**2 for x in range(5) if x % 2 == 0]
print(result)

A SyntaxError

B [1, 9, 25]

C [0, 4, 16]

D [0, 1, 4, 9, 16]

💡 Hint

The condition filters only even numbers before squaring.

Only 0, 2, and 4 are even in range(5). Their squares are 0, 4, and 16.

🧠 Conceptual

expert

Understanding list identity after slicing

Consider this code. What is the output of the print statement?

Python

a = [1, 2, 3, 4]
b = a[:]
b[0] = 100
print(a[0])

A 100

B TypeError

C IndexError

D 1

💡 Hint

Slicing creates a new list copy, so changes to b do not affect a.

b is a copy of a. Changing b[0] does not change a[0]. So a[0] remains 1.

Practice

1. Which of the following is the correct way to create an empty list in Python?

easy

A. ()

B. {}

C. []

D. list()

Solution

1. Step 1: Understand list syntax

   In Python, lists are created using square brackets [] or the list() function.

2. Step 2: Identify empty list creation

   [] is the literal syntax for an empty list, while list() also creates an empty list but is a function call.

3. Final Answer:

   [] -> Option C

4. Quick Check:

   Empty list = [] [OK]

Hint: Empty lists use square brackets [] directly [OK]

Common Mistakes:

• Using curly braces {} which create sets or dictionaries
• Using parentheses () which create tuples
• Confusing list() function with empty list literal

2. Which of the following is the correct syntax to create a list with the items 1, 2, and 3?

easy

A. list = [1, 2, 3]

B. list = <1, 2, 3>

C. list = {1, 2, 3}

D. list = (1, 2, 3)

Solution

1. Step 1: Recognize list syntax

   Lists in Python use square brackets [] to hold items in order.

2. Step 2: Check each option

   list = [1, 2, 3] uses square brackets with items 1, 2, 3 correctly. list = (1, 2, 3) uses parentheses which create tuples. list = {1, 2, 3} uses curly braces which create sets. list = <1, 2, 3> uses invalid syntax.

3. Final Answer:

   list = [1, 2, 3] -> Option A

4. Quick Check:

   List with items = [1, 2, 3] [OK]

Hint: Lists use square brackets [] with commas between items [OK]

Common Mistakes:

• Using parentheses () which create tuples
• Using curly braces {} which create sets
• Using invalid angle bracket syntax

3. What is the output of the following code?

my_list = [10, 'apple', 3.5]
print(my_list)

medium

A. [10, 'apple', 3.5]

B. (10, 'apple', 3.5)

C. {10, 'apple', 3.5}

D. 10, 'apple', 3.5

Solution

1. Step 1: Understand list contents and print

   The list my_list contains an integer, a string, and a float. Lists can hold mixed types.

2. Step 2: Print shows list with square brackets

   Printing a list shows its contents inside square brackets with commas separating items.

3. Final Answer:

   [10, 'apple', 3.5] -> Option A

4. Quick Check:

   Print list shows square brackets [OK]

Hint: Printed lists show square brackets and commas [OK]

Common Mistakes:

• Confusing list output with tuple or set syntax
• Expecting output without brackets
• Misreading quotes around strings

4. The following code is intended to create a list with numbers 1 to 3, but it causes an error. What is the problem?

numbers = [1, 2, 3
print(numbers)

medium

A. Using quotes around numbers

B. Using parentheses instead of square brackets

C. Missing commas between numbers

D. Missing closing square bracket ]

Solution

1. Step 1: Check list syntax

   The list starts with [ but does not have a closing ] bracket.

2. Step 2: Identify syntax error

   Missing the closing bracket causes a syntax error when Python tries to parse the list.

3. Final Answer:

   Missing closing square bracket ] -> Option D

4. Quick Check:

   Lists need matching brackets [OK]

Hint: Always match opening and closing brackets [] [OK]

Common Mistakes:

• Forgetting to close the list with ]
• Confusing brackets with parentheses
• Missing commas between items

5. You want to create a list that contains the numbers 1 to 5, but only even numbers should be included. Which code correctly creates this list?

hard

A. evens = [x for x in range(1, 6) if x % 2 != 0]

B. evens = [x for x in range(1, 6) if x % 2 == 0]

C. evens = [x for x in range(1, 5) if x % 2 == 1]

D. evens = [x for x in range(2, 7) if x % 2 == 1]

Solution

1. Step 1: Understand list comprehension with condition

   The code uses a list comprehension to select numbers from 1 to 5 (range(1, 6)) and filters only even numbers where x % 2 == 0.

2. Step 2: Check each option's condition and range

   evens = [x for x in range(1, 6) if x % 2 == 0] correctly uses range 1 to 5 and selects even numbers. Other options select odd numbers or wrong ranges.

3. Final Answer:

   evens = [x for x in range(1, 6) if x % 2 == 0] -> Option B

4. Quick Check:

   Even numbers filtered with x % 2 == 0 [OK]

Hint: Use list comprehension with if condition for filtering [OK]

Common Mistakes:

• Using wrong range limits
• Filtering odd numbers instead of even
• Confusing modulo condition