List creation and representation in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a list in Python?

A list in Python is a collection of items that are ordered and changeable. You can store multiple values in one variable.

beginner

How do you create an empty list in Python?

You create an empty list by using square brackets with nothing inside: [].

beginner

What will be the output of print([1, 2, 3])?

The output will be [1, 2, 3]. It shows the list with its elements inside square brackets separated by commas.

intermediate

How can you create a list with different types of items?

You can put different types of items inside a list, like numbers, strings, or even other lists: [1, 'apple', 3.14, [2, 3]].

beginner

What does the list ['a', 'b', 'c'] represent?

It represents a list of three string items: 'a', 'b', and 'c'. Lists keep the order of items as they are written.

Which symbol is used to create a list in Python?

A Parentheses ()

B Curly braces {}

C Angle brackets <>

D Square brackets []

Lists in Python are created using square brackets, like [1, 2, 3].

What will print([]) output?

A None

B An error

C An empty list: []

D Empty string

An empty list is shown as [] when printed.

Can a Python list contain items of different types?

A Only strings are allowed

B Yes, lists can hold mixed types

C Only numbers are allowed

D No, all items must be the same type

Python lists can contain any mix of types, like numbers, strings, or other lists.

What is the output of print([1, 2, 3][0])?

A 1

B 2

C 3

D [1, 2, 3]

The first item in the list is at position 0, so [1, 2, 3][0] is 1.

How do you represent a list with three string items 'a', 'b', and 'c'?

A ['a', 'b', 'c']

B {'a', 'b', 'c'}

C (a, b, c)

D <a, b, c>

Lists use square brackets and strings are in quotes: ['a', 'b', 'c'].

Explain how to create a list in Python and how it is shown when printed.

Think about the symbols and how items are arranged inside.

Describe what an empty list is and how you can create one.

It's like an empty box waiting to be filled.

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