List indexing and slicing in Python - Mini Project: Build & Apply

List Indexing and Slicing

📖 Scenario: You are organizing a small collection of your favorite fruits. You want to practice how to pick specific fruits from the list using their positions.

🎯 Goal: Learn how to use list indexing and slicing to select individual items and groups of items from a list.

📋 What You'll Learn

Create a list with exact fruit names

Create variables to hold specific index positions

Use list indexing to get a single fruit

Use list slicing to get a group of fruits

Print the selected fruits

💡 Why This Matters

🌍 Real World

Selecting items from a list is like picking fruits from a basket by their position. This helps when you want to work with parts of a collection.

💼 Career

Understanding list indexing and slicing is essential for data handling, filtering, and processing in many programming jobs.

1

Create the fruit list

Create a list called fruits with these exact items in order: 'apple', 'banana', 'cherry', 'date', 'elderberry'.

Python

# Create the list called fruits with the exact items
# Your code here

Hint

Remember to use square brackets [] to create a list and separate items with commas.

2

Set index variables

Create two variables: first_index set to 0 and slice_start set to 1.

Python

fruits = ['apple', 'banana', 'cherry', 'date', 'elderberry']
# Create first_index = 0 and slice_start = 1
# Your code here

Hint

Just assign the numbers 0 and 1 to the variables as shown.

3

Use indexing and slicing

Create a variable first_fruit that gets the fruit at first_index from fruits. Then create a variable some_fruits that slices fruits from slice_start up to (but not including) 4.

Python

fruits = ['apple', 'banana', 'cherry', 'date', 'elderberry']
first_index = 0
slice_start = 1
# Get first_fruit using fruits[first_index]
# Get some_fruits using fruits[slice_start:4]
# Your code here

Hint

Use square brackets with the index variable for single item, and with start:end for slicing.

4

Print the selected fruits

Print first_fruit and some_fruits each on its own line.

Python

fruits = ['apple', 'banana', 'cherry', 'date', 'elderberry']
first_index = 0
slice_start = 1
first_fruit = fruits[first_index]
some_fruits = fruits[slice_start:4]
# Print first_fruit and some_fruits
# Your code here

Hint

Use two print statements, one for each variable.

Practice

1. What does the expression my_list[2] return when my_list = [10, 20, 30, 40, 50]?

easy

A. 40

B. 20

C. 30

D. 50

Solution

1. Step 1: Understand list indexing

   Indexing starts at 0, so my_list[0] is 10, my_list[1] is 20, and my_list[2] is 30.

2. Step 2: Identify the value at index 2

   The value at index 2 is 30.

3. Final Answer:

   30 -> Option C

4. Quick Check:

   Index 2 value = 30 [OK]

Hint: Remember indexing starts at zero, so count from 0 [OK]

Common Mistakes:

• Starting count from 1 instead of 0
• Confusing index 2 with index 3
• Mixing up values and indexes

2. Which of the following is the correct syntax to get the last element of a list nums using indexing?

easy

A. nums[last]

B. nums[1]

C. nums[len(nums)]

D. nums[-1]

Solution

1. Step 1: Recall negative indexing

   Negative indexes count from the end, so -1 means the last element.

2. Step 2: Check each option

   nums[-1] uses nums[-1], which correctly accesses the last element. nums[1] accesses the second element. nums[last] is invalid syntax. nums[len(nums)] causes an IndexError because list indexes go from 0 to len(nums)-1.

3. Final Answer:

   nums[-1] -> Option D

4. Quick Check:

   Last element index = -1 [OK]

Hint: Use -1 to get the last item in a list [OK]

Common Mistakes:

• Using len(nums) as index (out of range)
• Trying to use 'last' as an index
• Confusing positive and negative indexes

3. What is the output of this code?

letters = ['a', 'b', 'c', 'd', 'e']
print(letters[1:4])

medium

A. ['b', 'c', 'd']

B. ['c', 'd', 'e']

C. ['b', 'c', 'd', 'e']

D. ['a', 'b', 'c']

Solution

1. Step 1: Understand slicing syntax

   Slicing letters[1:4] means start at index 1 up to but not including index 4.

2. Step 2: Identify elements at indexes 1, 2, 3

   Index 1 is 'b', index 2 is 'c', index 3 is 'd'. So the slice is ['b', 'c', 'd'].

3. Final Answer:

   ['b', 'c', 'd'] -> Option A

4. Quick Check:

   Slicing excludes stop index [OK]

Hint: Slice stops before the stop index, not including it [OK]

Common Mistakes:

• Including the stop index element
• Confusing start and stop indexes
• Using wrong indexes for slicing

4. The code below causes an error. What is the problem?

nums = [1, 2, 3, 4, 5]
print(nums[5])

medium

A. SyntaxError due to wrong brackets

B. IndexError because index 5 is out of range

C. TypeError because nums is not a list

D. No error, prints 5

Solution

1. Step 1: Check list length and valid indexes

   List nums has 5 elements with indexes 0 to 4.

2. Step 2: Understand index 5 usage

   Index 5 is outside the valid range, so accessing nums[5] causes an IndexError.

3. Final Answer:

   IndexError because index 5 is out of range -> Option B

4. Quick Check:

   Index must be less than list length [OK]

Hint: Indexes go from 0 to length-1 only [OK]

Common Mistakes:

• Thinking index 5 is valid for 5 elements
• Confusing SyntaxError with IndexError
• Assuming list indexes start at 1

5. Given data = [5, 10, 15, 20, 25, 30], which expression returns a new list with every second element in reverse order?

hard

A. data[::-2]

B. data[::2]

C. data[-2::-1]

D. data[1::2]

Solution

1. Step 1: Understand slicing with step and negative step

   The slice data[::-2] starts from the end and takes every second element backwards.

2. Step 2: Check what data[::-2] returns

   It returns [30, 20, 10], which is every second element in reverse order.

3. Step 3: Verify other options

   data[::2] returns every second element forward: [5, 15, 25]. data[-2::-1] returns from index -2 backwards: [25, 20, 15, 10, 5]. data[1::2] returns every second element starting at index 1: [10, 20, 30].

4. Final Answer:

   data[::-2] -> Option A

5. Quick Check:

   Negative step reverses and skips elements [OK]

Hint: Use negative step to reverse and skip elements [OK]

Common Mistakes:

• Using positive step for reverse
• Confusing start index with step sign
• Misunderstanding slice boundaries