List Slicing in Python: Syntax and Examples

Slicing a list in Python means extracting a portion (or subsequence) of the list using a specific syntax:

Syntax:

list[start:stop:step]

• start: index to begin slicing (inclusive)
• stop: index to end slicing (exclusive)
• step: how many elements to skip (default is 1)

Examples:

numbers = [10, 20, 30, 40, 50, 60, 70]

1. Get elements from index 1 to 4:

numbers[1:5]   # [20, 30, 40, 50]

2. Get every second element:

numbers[::2]   # [10, 30, 50, 70]

3. Reverse the list:

numbers[::-1]  # [70, 60, 50, 40, 30, 20, 10]

4. From index 3 to end:

numbers[3:]    # [40, 50, 60, 70]

5. From start to index 4:

numbers[:5]    # [10, 20, 30, 40, 50]

📺 Video Tutorial: List Slicing

The video explains how to modify a list by replacing multiple elements with a single element.

This video covers:

• ✔️ A list called "list1" is created with five integers [00:07].
• ✔️ The second, third, and fourth elements of the list (98, 23, and 70) are selected using slice notation [00:13].
• ✔️ These elements are replaced with the single element 20 [00:23].
• ✔️ The modified list is printed [00:29].

{% assign video_type = "video" %} {% assign video_id = "uvdT5kczvCg" %} {% include youtube-video.html video_type=video_type video_id=video_id %}

Tasks

1. Positive Index Slicing

   • Given numbers = [10, 20, 30, 40, 50, 60], extract:
     • First 3 elements
     • Elements from index 2 to 4
     • Last 2 elements (using positive indices)

2. Negative Index Practice

   • For letters = ['a', 'b', 'c', 'd', 'e', 'f']:
     • Get all elements except the last one using negative indexing
     • Extract ['c', 'd'] using negative indices
     • Get the last element using negative index

3. Step Value Exercises

   • Using data = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]:
     • Extract all even-indexed items (0, 2, 4...)
     • Get every 3rd item starting from index 1
     • Reverse the list using step value